This problem is not limited to XBMC, nor is it limited to nVidia graphics cards; it has been reported on Intel as well, and possibly ATI/AMD.
Try the suggestion below (from the referenced source):
The real problem is with the libsdl1.2 package, as stated in this bug report.
The solution is ready, but somehow isn't available on default Ubuntu package sources yet (at least not for me). So, a way to solve this is to import the developer PPA and install the patched package directly:
sudo apt-add-repository ppa:timo-jyrinki/ppa sudo apt-get update sudo apt-get install libsdl1.2debian
You can later remove the PPA with:
sudo apt-get install ppa-purge sudo ppa-purge ppa:timo-jyrinki/ppa