I've recently tried out 4.2rc1 and I tried turning on the composition support in xfwm4 and it's messed up with the latest nvidia drivers (66.29). I've tried on another computer with older drivers (44.96) and with the Xephyr nested X server and both of those work fine, so it's a specific interaction with the these drivers. What happens is that all the windows disapper (as is usual when they are initially redirected) but then they never appear again - I just see the desktop and nothing else. I can still interact with the invisible windows but there's no visual activity. Obviously some of the blame has to lie with the nvidia drivers, but xcompmgr works fine, so it's not an unavoidable problem.
NVidia drivers are very buggy, that a sad but proven fact. I doubt it's a problem with xfwm4 since it works fine here (with NVidia btw)
Can you try this one, I'm really not seeing anuthing wrong: http://www.xfce.org/~olivier/packages/xfwm4-4.1.99.2.tar.gz BTW, I'm decreasing severity to minor, the compositor is not critical and not even enabled by default.
ok, the only explanation I see is the following: xfwm4 uses an additional buffer for redering the screen, and I suspect that your video card runs out of mem for some reason (did you try reducing the resolution?) BTW, I removed that additional buffer, so things might have improve. If not, ahumm, that prolly stay as "won't fix" because it works for me and I have no idea what else could be wrong.
btw, you can try the following source that includes the "fix": http://www.xfce.org/~olivier/packages/xfwm4-4.1.99.2.tar.gz
i'm almost certain this is a bug with the latest nvidia drivers. i had the same problem, you mention, and rolled back to the previous version, and it was fine. i did a bunch of googling, and it seemed to confirm that. note that (for me at least), the problem exists regardless of whether or not composite is enabled. it seems to be a compatibility problem specific to nvidia v6629 and x.org 6.8.x.
With the compositor disabled (at runtime, still compiled in), it works fine - just to respond to Brian's comment. I tried your tweaked build and it didn't help - so I doubt it's a lack of memory issue - which I suspect would manifest itself rather more spectacularly, and I assume the nvidia drivers would use agp if they needed to anyway. Oh well. I wouldn't mind downgrading if it wasn't for the fact that older versions of the drivers are basically guaranteed to crash the X server within 20 minutes. :-)
Ok, from the discussion I conclude this is a bug in XOrg/Nvidia driver, so I'm closing it now.