A DESCRIPTION OF THE PROBLEM :
The sum of pixel-snapped child widths of HBox/VBox don't always snap to the same value as the width or height of the container itself. This can lead to a visual glitch where the content of a HBox or VBox either doesn't fill the container, or extends slightly beyond its bounds.

The sample program shows the problem for both cases.


---------- BEGIN SOURCE ----------
Region r1 = new Region();
Region r2 = new Region();
Region r3 = new Region();
Region r4 = new Region();
Region r5 = new Region();
Region r6 = new Region();
r1.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
r2.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
r3.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
r4.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
r5.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
r6.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
r1.setPrefWidth(25.3);
r2.setPrefWidth(25.3);
r3.setPrefWidth(25.4);
r4.setPrefWidth(25.3);
r5.setPrefWidth(25.3);
r6.setPrefWidth(25.4);
r1.setMaxHeight(30);
r2.setMaxHeight(30);
r3.setMaxHeight(30);
r4.setMaxHeight(30);
r5.setMaxHeight(30);
r6.setMaxHeight(30);
HBox hbox1 = new HBox(r1, r2, r3, r4, r5, r6);
hbox1.setBackground(new Background(new BackgroundFill(Color.RED, null, null)));
hbox1.setPrefHeight(40);

r1 = new Region();
r2 = new Region();
r3 = new Region();
r4 = new Region();
r5 = new Region();
r6 = new Region();
r1.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
r2.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
r3.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
r4.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
r5.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
r6.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
r1.setPrefWidth(25.3);
r2.setPrefWidth(25.3);
r3.setPrefWidth(25.4);
r4.setPrefWidth(25.3);
r5.setPrefWidth(25.3);
r6.setPrefWidth(25.4);
r1.setMaxHeight(30);
r2.setMaxHeight(30);
r3.setMaxHeight(30);
r4.setMaxHeight(30);
r5.setMaxHeight(30);
r6.setMaxHeight(30);
HBox hbox2 = new HBox(r1, r2, r3, r4, r5, r6);
hbox2.setBackground(new Background(new BackgroundFill(Color.RED, null, null)));
hbox2.setPrefHeight(40);
hbox2.setPrefWidth(152);

VBox root = new VBox(new HBox(hbox1), new HBox(hbox2));
root.setSpacing(20);
Scene scene = new Scene(root, 500, 250);

primaryStage.setScene(scene);
primaryStage.show();
---------- END SOURCE ----------