glClientWaitSync always finish gl pipeline


it seems, that glClientWaitSync always finish the gl pipeline although the fence is already fired. I tried it in this way:

GLsync sync = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
glFinish(); // be sure, sync is fired
glClientWaitSync(sync, GL_SYNC_FLUSH_COMMANDS_BIT, 0); // return GL_ALREADY_SIGNALED

I think, the glClientWaitSync call must not block, but nsight shows that it finish the pipeline.

What may I do wrong here? Or may it be a driver issue?

My specs:
Windows 8 x64
GeForce GTX 660 Ti
Version 310.90
64bit binary

Where would I have to create a bug report for such issues? As glClientWaitSync(timeout=0) must not block, this is a driver issue.

The “Report an Issue” link on is broken and really no one cares about the official forum?
NVIDIA, please, I want to fix such issues instead of having to say to everyone “don’t use nvidia”