Created attachment 766 [details]
Test case to reproduce
The position of the window is wrong after a resize in its container (e.g. another component has been made visible in the same container).
Described also here:
Reproducible on Mac OS X El Capitan with JDK 1.8.0_60.
Attached is a simple test-case to reproduce it. It shows a JFrame with Gears and a button at the top. When the button is clicked it makes a panel at the south visible and you can observer the position of the glwindow being wrong.