FULL PRODUCT VERSION :
java version "1.8.0_101"
Java(TM) SE Runtime Environment (build 1.8.0_101-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
windows 7 64 bit

EXTRA RELEVANT SYSTEM CONFIGURATION :
Seems the bug is similar to the one described in: https://bugs.openjdk.java.net/browse/JDK-8156049

I can confirm that this bug started in release 1.8.0_92 and still exists in the current version. It was closed on the page...it shouldn't have been. the bug is still there.

A DESCRIPTION OF THE PROBLEM :
The bug is the same as described in: https://bugs.openjdk.java.net/browse/JDK-8156049

it was closed, but I assure you this still exists.
The treetable doesn't clean up the icons after the table is collapsed.

This started in 1.8.0_92. I was hoping since the bug was filed it would be fixed, it hasn't yet, I checked the page for progress and it was closed.

I'm confirming that this is a bug that wasn't fixed and I can reproduce it...

REGRESSION. Last worked in version 8u91

ADDITIONAL REGRESSION INFORMATION:
java version "1.8.0_101"
Java(TM) SE Runtime Environment (build 1.8.0_101-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
the original bug report describes how to reproduce it: https://bugs.openjdk.java.net/browse/JDK-8156049

This shouldn't have been closed.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The images for the collapsed child nodes should disappear when the parent node is collapsed.
ACTUAL -
The icons of the collapsed nodes remain leaving a visual mess.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
no crash logs.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.beans.property.ReadOnlyStringWrapper;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.TreeTableColumn;
import javafx.scene.control.TreeTableColumn.CellDataFeatures;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeTableView;
import javafx.stage.Stage;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;

public class TreeTableViewSample extends Application {
    private static final Image icon = new Image(TreeTableViewSample.class.getResourceAsStream("icon.png"));

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

    @Override
    public void start(Stage stage) {
        stage.setTitle("Tree Table View Samples");
        final Scene scene = new Scene(new Group(), 200, 400);
        Group sceneRoot = (Group)scene.getRoot();

        //Creating tree items
        final TreeItem<String> childNode1 = new TreeItem<>("Child Node 1", new ImageView(icon));
        final TreeItem<String> childNode2 = new TreeItem<>("Child Node 2", new ImageView(icon));
        final TreeItem<String> childNode3 = new TreeItem<>("Child Node 3", new ImageView(icon));

        //Creating the root element
        final TreeItem<String> root = new TreeItem<>("Root node", new ImageView(icon));
        root.setExpanded(true);

        //Adding tree items to the root
        root.getChildren().setAll(childNode1, childNode2, childNode3);

        //Creating a column
        TreeTableColumn<String,String> column = new TreeTableColumn<>("Column");
        column.setPrefWidth(150);

        //Defining cell content
        column.setCellValueFactory((CellDataFeatures<String, String> p) ->
            new ReadOnlyStringWrapper(p.getValue().getValue()));

        //Creating a tree table view
        final TreeTableView<String> treeTableView = new TreeTableView<>(root);
        treeTableView.getColumns().add(column);
        treeTableView.setPrefWidth(152);
        treeTableView.setShowRoot(true);
        sceneRoot.getChildren().add(treeTableView);
        stage.setScene(scene);
        stage.show();
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
none working for me.
Fix the bug.