As can be read here : http://www.nvnews.net/vbulletin/showthread.php?t=79235
The machine is running FreeBSD 6.1-RELEASE with X.org 7.2-RC2. GPU is NV28 (GeForce4 Ti4200 Go AGP 8x).
I've tried 9625, 9626, 9629 and 9631 but they all show the same problem.
I've recompiled beryl (just for the sake of it), but it didn't change anything.
Edit: It's not a FreeBSD/beryl issue cause I have it running with 9742 and NV3X/NV4X GPUs.