Minimum size is not used properly in layout, but it is in rendering. The result is that parent bounds appear to be miscalculated.

Try the following:


package layoutbounds;

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.geometry.Bounds;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Priority;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

/**
 * Resize the child by dragging the green square. JavaFX 2.2 and JavaFX 8
 * behave very differently.
 * @author scott.palmer
 */
public class LayoutBounds extends Application {

    static class Widget extends AnchorPane {

        private final VBox vbox;
        private final BorderPane contentPane;
        private final AnchorPane contentStack;
        private final StackPane contentWrapper;
        private final AnchorPane childrenGroup;
        private final AnchorPane connectionGroup;
        private final HBox bottomPane;

        public Widget(String title) {
            vbox = new VBox();
            vbox.setFillWidth(true);
            vbox.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
            AnchorPane.setTopAnchor(vbox, 0.0);
            AnchorPane.setRightAnchor(vbox, 0.0);
            AnchorPane.setBottomAnchor(vbox, 0.0);
            AnchorPane.setLeftAnchor(vbox, 0.0);
            getChildren().add(vbox);

            Label titleBar = new Label(title);
            titleBar.setAlignment(Pos.CENTER);
            titleBar.setMaxWidth(Double.MAX_VALUE);
            titleBar.setTextFill(Color.WHITE);
            titleBar.setStyle("-fx-background-color: BLUE;");
            vbox.getChildren().add(titleBar);

            contentStack = new AnchorPane();
            contentWrapper = new StackPane();

            bottomPane = new HBox();
            bottomPane.getChildren().add(new Label("resize->"));
            
            contentPane = new BorderPane();
            contentPane.setBottom(bottomPane);
            contentPane.setPickOnBounds(false);

            childrenGroup = new AnchorPane();
            contentWrapper.getChildren().add(childrenGroup);
            contentPane.setCenter(contentWrapper);

            connectionGroup = new AnchorPane();

            AnchorPane.setTopAnchor(contentPane, 0.0);
            AnchorPane.setRightAnchor(contentPane, 0.0);
            AnchorPane.setBottomAnchor(contentPane, 0.0);
            AnchorPane.setLeftAnchor(contentPane, 0.0);

            contentStack.getChildren().add(connectionGroup);
            contentStack.getChildren().add(contentPane);
            contentStack.setMaxHeight(Double.MAX_VALUE);
            VBox.setVgrow(contentStack, Priority.ALWAYS);
            vbox.getChildren().add(contentStack);

            Rectangle sizer = new Rectangle(16, 16);
            sizer.setFill(Color.GREENYELLOW);
            AnchorPane.setRightAnchor(sizer, 0.0);
            AnchorPane.setBottomAnchor(sizer, 0.0);
            getChildren().add(sizer);
            
            sizer.setOnMouseDragged(resizeDragHandler);
            setStyle("-fx-background-color: SKYBLUE; -fx-border-color: YELLOW; -fx-border-width: 3px;");
        }

        void addComponent(Widget child) {
            childrenGroup.getChildren().add(child);
        }

        private EventHandler<MouseEvent> resizeDragHandler = new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent me) {
                Point2D dragPoint = Widget.this.sceneToLocal(new Point2D(me.getSceneX(), me.getSceneY()));
                sizeToPoint(dragPoint);
                me.consume();
            }
        };
        private void sizeToPoint(Point2D dragPoint) {
            Bounds bounds = getBoundsInLocal();
            setMinSize(Math.max(0, dragPoint.getX()-bounds.getMinX()),
                       Math.max(0, dragPoint.getY()-bounds.getMinY()));
        }
    }
    
    @Override
    public void start(Stage primaryStage) {
        Widget rectA = new Widget("Parent");
        Widget rectB = new Widget("Child");
        rectA.addComponent(rectB);
        AnchorPane root = new AnchorPane();
        root.getChildren().add(rectA);
        Scene scene = new Scene(root, 400, 300);
        primaryStage.setTitle("Layout Bounds Issues");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}