the following code illustrates a problem in the way Region's layout code is always trying to snap positions, regardless of whether the node is resizable and can even be snapped:

            StackPane stack = new StackPane();
            stack.setAlignment(Pos.BOTTOM_RIGHT); // leaves a small gap on bottom-right of circle because of snap-to-pixel rounding
            stack.setStyle("-fx-background-color: yellow;");
            stack.getChildren().add(new Circle(20.12));