nVidia 9631 black screen freeze upon startx

[sasq]

Howdy.

After I've emerged new nVidia beta drivers [I'm trying to use Beryl ;J] strange things are happening :/
I can startx only once, because when I stop X-server and start it again using startx command, I got black screen and no nVidia logo, and my computer hangs totally [I can't even switch to other terminal to reboot gracefully]. I'm forced to use reset switch and after that all works properly [so startx works only first time after reboot].
I have checked my X.org logs, but there are no errors. What could be wrong?

I have GeForce4 MX 440 and I use nvidia-drivers-1.0.9631 and 2.6.16-gentoo-r13 kernel.

UPDATE:
I've checked some things and it shows out that the problem occurs only if the last used window-manager was Fluxbox :/ When I use plain X command to start X-server, everything work fine and I can turn X-server on and off multiple times without problems. The same is when I use different window-managers. But when I use Fluxbox, turn it off and try to launch X-server again, it freezes on black screen before displaying nVidia splash.
What's wrong with Fluxbox and nVidia together?
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SasQ