Run the attached test with jdk8 on Linux with opengl enabled:
java -Dsun.java2d.opengl=True JPanelTest

Once in a while -- sometimes every other time, sometimes once in five times -- paint is not performed or performed not in full. It looks like a timing issue while trying to calculate a dirty region.

I tried it on Ubuntu 12.04 i586 and x64 with Nvidia and ATI drivers and also on some OEL 6.3 with ATI, all with the similar results.
Not reproducible on OS X (10.8) nor on Windows (tried 7x64).

Note about the test: the sleep added at the end may be changed to realSync() on Gnome but should not on Xfce and Windows.