FULL PRODUCT VERSION :
1.8 u121 x64

ADDITIONAL OS VERSION INFORMATION :
Windows 8.1 x64

A DESCRIPTION OF THE PROBLEM :
GridPane has problems with Nodes with ColSpan and PrefSize

create 2 Columns with PrefSize
every column chaange size to an day Label (day of week)

add a new Label with
- colSpan = 2
- minWidth to USE_PREF_SIZE
- text large as 2 existing columns

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
employeeCount = 1
2 Columns generated
first column set size to [X] Label
second column span to size from label [longlonglong]
http://194.25.240.197:9980/gridpane.layout.work.png

employeeCount = 2
last column dont change size to label [longlonglong]
http://194.25.240.197:9980/gridpane.layout.not.work.png


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
resize columns to ColSpan Label
ACTUAL -
in some cases the Columns dont change its size
the ColSpan Labels is overlab tu next / prev Columns

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package GridPaneLayout;

import java.time.DayOfWeek;
import java.time.format.DateTimeFormatter;
import java.util.LinkedList;
import java.util.List;

import com.sun.javafx.css.StyleManager;

import javafx.application.Application;
import javafx.geometry.HPos;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.geometry.VPos;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.ColumnConstraints;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.Priority;
import javafx.scene.layout.RowConstraints;
import javafx.stage.Stage;

/** @author sst */
public class GridPaneLayoutMain extends Application {

    private static final double MAX_VALUE = Double.MAX_VALUE;
    private static final double USE_PREF_SIZE = Double.NEGATIVE_INFINITY;
    private static final double USE_COMPUTED_SIZE = -1.0;
    private static final String CSS = GridPaneLayoutMain.class.getResource("Planung.css").toExternalForm();
    private static final DateTimeFormatter DAY = DateTimeFormatter.ofPattern("EEE");

    public static void main(String[] args) {
        StyleManager.getInstance().addUserAgentStylesheet(CSS);
        launch(GridPaneLayoutMain.class, args);
    }

    @Override
    public void start(final Stage primaryStage) throws Exception {
        // Grid
        final GridPane grid = new GridPane();
        grid.setMinSize(USE_PREF_SIZE, USE_PREF_SIZE);
        grid.setPrefSize(USE_COMPUTED_SIZE, USE_COMPUTED_SIZE);
        grid.setMaxSize(USE_PREF_SIZE, USE_PREF_SIZE);
        grid.setPadding(new Insets(4));
        grid.getStylesheets().add(CSS);

        // Root
        final BorderPane root = new BorderPane();
        root.setCenter(new ScrollPane(grid));

        // Create
        final Button create = new Button("create");
        root.setTop(create);
        create.setOnAction((event) -> grid(grid));

        // show
        primaryStage.setScene(new Scene(root, 400, 400));
        primaryStage.show();
    }

    private final void grid(final GridPane grid) {
        // clear
        grid.getChildren().clear();
        grid.getColumnConstraints().clear();
        grid.getRowConstraints().clear();

        final int sectionCount = 1;
        // 1 works, > 1 triggers layouting problem
        final int employeeCount = 2;
        final int dayOfWeeks = 2;
        final List<Node> nodes = new LinkedList<>();

        int rowIndex = 0;
        int columnIndex = 0;

        // for all section
        for (int si = 0; si < sectionCount; si++) {
            // Start index for section
            final int sectionIndex = columnIndex;

            // Span of section
            // employeeCount * (dayOfWeeks for employee)
            // not all employees have the same [dayOfWeek]
            // possible fomr 1 to 5
            int sectionSpan = 0;

            // for all employee in this section
            for (int ei = 0; ei < employeeCount; ei++) {
                rowIndex = 3;

                nodes.add(createEmployeeLabel(columnIndex, dayOfWeeks, si, ei));

                for (int d = 0; d < dayOfWeeks; d++) {
                    nodes.add(createHeaderDayLabel(columnIndex + d, d));
                    sectionSpan++;
                }

                // Holiday
                {
                    nodes.add(createHolidayLabel(rowIndex++, columnIndex));
                }

                // leave
                {

                }

                // work
                {
                    nodes.add(createWorkLabel("long\nlong", rowIndex++, columnIndex, 2));
                    nodes.add(createWorkLabel("longlonglong", rowIndex++, columnIndex, 2));
                    // nodes.add(createWorkLabel("_", rows++, columnIndex + 1,
                    // 1));
                }

                // Empty
                {
                    nodes.add(createEmptyLabel(rowIndex++, columnIndex, dayOfWeeks));
                    // nodes.add(createEmptyLabel(rows++, dataIndex,
                    // dayOfWeeks));
                    // nodes.add(createEmptyLabel(rows++, dataIndex,
                    // dayOfWeeks));
                }

                // next empleyee is current + days per week
                columnIndex += dayOfWeeks;
            }

            // create last
            // on this position the current CollSpan for Section is calculated
            nodes.add(createSectionLabel(si, sectionIndex, sectionSpan));
        }

        // constraints
        for (int r = 0; r < rowIndex; r++) {
            grid.getRowConstraints().add(new RowConstraints(USE_PREF_SIZE, USE_COMPUTED_SIZE, MAX_VALUE, Priority.NEVER, VPos.CENTER, true));
        }

        for (int c = 0; c < columnIndex; c++) {
            grid.getColumnConstraints().add(new ColumnConstraints(USE_PREF_SIZE, USE_COMPUTED_SIZE, MAX_VALUE, Priority.NEVER, HPos.CENTER, true));
        }

        grid.getChildren().addAll(nodes);
    }

    // Headers#############################################################################################################################

    private final GridLabel createSectionLabel(final int si, final int sectionIndex, final int sectionSpan) {
        final GridLabel label = new GridLabel("Section " + si, "planung-header", "planung-header-bereich");
        label.setIndex(0, sectionIndex);
        label.setSpan(1, sectionSpan);
        return label;
    }

    private final GridLabel createEmployeeLabel(final int column, final int span, final int si, final int mi) {
        final GridLabel label = new GridLabel("M." + si + "." + mi, "planung-header", "planung-header-mitarbeiter");
        label.setIndex(1, column);
        label.setSpan(1, span);
        return label;
    }

    private final GridLabel createHeaderDayLabel(final int column, final int day) {
        final GridLabel label = new GridLabel(DAY.format(DayOfWeek.of(day + 1)), "planung-header", "planung-header-tag");
        label.setIndex(2, column);
        return label;
    }

    // Data################################################################################################################################

    private final GridLabel createHolidayLabel(final int row, final int column) {
        final GridLabel label = new GridLabel("X", "planung-item", "planung-feiertag", "planung-abwesenheit");
        label.setIndex(row, column);
        return label;
    }

    private final GridLabel createEmptyLabel(final int row, final int column, final int span) {
        final GridLabel label = new GridLabel(null, "planung-item");
        label.setIndex(row, column);
        label.setSpan(1, span);
        return label;
    }

    private final GridLabel createWorkLabel(final String action, final int row, final int column, final int span) {
        final GridLabel label = new GridLabel(action, "planung-item", "planung-planung");
        label.setIndex(row, column);
        label.setSpan(1, span);
        return label;
    }

    // classes#############################################################################################################################

    /** @author sst */
    private static final class GridLabel extends Label {

        private static final Insets BORDER = new Insets(4);

        private GridLabel(final String text, final String... css) {
            // Label
            super();

            // Cache
            this.setCache(true);

            // Size
            setMinSize(USE_PREF_SIZE, USE_PREF_SIZE);
            setPrefSize(USE_COMPUTED_SIZE, USE_COMPUTED_SIZE);
            setMaxSize(MAX_VALUE, MAX_VALUE);

            // Border
            setPadding(BORDER);

            // Text Position
            setAlignment(Pos.CENTER);

            // Grid Settings
            setIndex(0, 0);
            setSpan(1, 1);

            // CSS
            addCssClasses("planung-base");
            addCssClasses(css);

            setText(text);
        }

        private final void setIndex(final int row, final int column) {
            GridPane.setRowIndex(this, Integer.valueOf(row));
            GridPane.setColumnIndex(this, Integer.valueOf(column));
        }

        private final void setSpan(final int row, final int column) {
            GridPane.setRowSpan(this, Integer.valueOf(row));
            GridPane.setColumnSpan(this, Integer.valueOf(column));
        }

        private final void addCssClasses(final String... cssClasses) {
            getStyleClass().addAll(cssClasses);
        }
    }
}

------------------
/* Planung.css */

.planung-base{
-fx-border-color: black !important;
-fx-border-insets: -1px 0px 0px -1px !important;
}

.planung-header{
-fx-font-weight: bold !important;
-fx-background-color: #E6E6E6 !important;
}

.planung-header-bereich{
/* top, right, bottom, and left */
-fx-border-width: 1px 1px 0px, 1px !important;
}

.planung-header-mitarbeiter{
/* top, right, bottom, and left */
-fx-border-width: 0px 1px 0px, 1px !important;
}

.planung-header-tag{
/* top, right, bottom, and left */
-fx-font-weight: normal !important;
-fx-font-size: 10 !important;
-fx-border-width: 0px 1px 1px, 1px !important;
}

.planung-datum{
  /* top, right, bottom, and left */
  -fx-border-width: 1px 1px 1px, 1px !important;
}

.planung-item{
/* top, right, bottom, and left */
-fx-border-width: 1px 1px 1px, 1px !important;
}

.planung-feiertag{
-fx-text-fill: orangered ;
}

.planung-abwesenheit{
-fx-background-color: silver !important;
}

.planung-planung{
  -fx-text-fill: black;
}

---------- END SOURCE ----------