This is reproducible with new scenegraph build on Ubuntu 8.04. Not reproducible with marina b10.

Run the below program. It shows three rectangles and a textbox, all in a group. On clicking any node, node.toFront is called. On clicking the textbox, sometimes, it shows painting artifacts - with some portion of a node on top and some below. Attached is a screenshot.

import javafx.stage.*;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.text.*;
import javafx.scene.shape.*;
import javafx.scene.paint.*;
import javafx.scene.input.*;

var rect1: Rectangle = Rectangle {
    x: 50
    y: 125
    width: 50
    height: 60
    arcWidth: 20
    arcHeight: 20
    fill: Color.BLACK
    onMousePressed: function( e: MouseEvent ):Void {
        rect1.toFront();
    }
};

var rect2: Rectangle = Rectangle {
    x: 60
    y: 150
    width: 50
    height: 60
    arcWidth: 20
    arcHeight: 20
    fill: Color.RED
    onMousePressed: function( e: MouseEvent ):Void {
        rect2.toFront();
    }
};

var rect3: Rectangle = Rectangle {
    x: 70
    y: 175
    width: 50
    height: 60
    arcWidth: 20
    arcHeight: 20
    fill: Color.YELLOW
    onMousePressed: function( e: MouseEvent ):Void {
        rect3.toFront();
    }
};
var textBox1: TextBox = TextBox {
    text: "Hi!! I'm inside the Rect Group!!!"
    columns: 20
    selectOnFocus: true
    editable: true
    translateX: 90
    translateY: 200
    blocksMouse: false
    onMousePressed: function( e: MouseEvent ):Void {
        textBox1.toFront();
    }
        
};
var rectGroup: Group = Group {
    content: [rect1, rect2, rect3, textBox1]
    onMousePressed: function( e: MouseEvent ):Void {
        rectGroup.toFront();
    }
};

var appFrame = Stage {
    scene: Scene {
        content: rectGroup
        width: 400
        height: 400
    }
};