There are multiple manifestations of this problem. One way to reproduce this is:

1. Run HelloStyledPopups

java -Djdk.gtk.verbose=true -Djdk.gtk.version=3 -cp apps/toys/Hello/dist/Hello.jar hello.HelloStyledPopups

2. Click on the "Yello Menu"

3. Select one of the menu items

4. Click on the "Yellow Popup" ComboBox

5. Slowly drag the menu down the choices

BUG: you will see the "Yellow" menu become highlighted at some point, as if glass is confused about the mouse location

6. Click somewhere in the window of the program to deselect the popup

7. Click on the "Yellow Popup" ComboBox

8. Move the mouse down and as soon as you see the "Yellow" menu become highlighted, click the mouse

BUG: sometimes when you do this, the list of MenuItems will briefly popup