This issue is seen when metal ( -Dsun.java2d.metal=true) is turned on. This works as expected in OpenGL is turn on

1) Run the attached test case
2) When is frame is visible with components.
3) Click multiple times on Editable JComboBox arrow button.
4) Click on "Add/Remove Items" button
5) Click on the ComboBox if you see the combobox popup gray then the bug is reproduced.

Note: You need to repeat Step(3) to step(5) multiple times.

I have attached the screenshot of the issue.