Hi, when having a window with a transparent background, I can observe a lot of graphical bugs. These bugs include for example parts of screen not rendered and color pixels in random place on the application window. To reproduce, load attached testcase as toplevel window; then click on "third choice" and let mouse button pressed. The line: second choice flickers and disappears. It appears back when releasing keypress. I investigated a bit, and this is because clicking will call invalidateRoot. When releasing, the reflow happens, and line is correctly displayed again.