I also upgraded Ubuntu on our media PC. After the upgrade XBMC started to act strangely. When I tried to move up or down in the menu, it jumped two for each keypress. During the playback, sometimes the video froze for a fraction of the second, while the sound was continuing normally, then the video fast forwarded and caught up with the audio. The third issue was that the OSD wasn’t visible. It appeared for a quick moment, but then it disappeared. It was still there, but it wasn’t visible.
The first issue was caused by the new kernel, which detects certain RC keypresses as keyboard events. This means the up arrow is received twice by XBMC, once as RC up and once as keyboard up. This can be solved by disabling using RC keypresses as keyboard events. For example adding the following line to /etc/rc.local:
echo none +lirc > /sys/class/rc/rc0/protocols
The other two issues were caused by the OpenGL driver. In the media PC we have a Radeon 4350 (RV710) card. In the latest Ubuntu the original Mesa DRI driver was replaced by the Gallium DRI driver. Fortunately the original driver is still installed:
$ dpkg -L libgl1-mesa-dri |grep r600
/usr/lib/dri/r600_dri.so
/usr/lib/dri-alternates/r600_dri.so
Simply removing the first one and rebooting the PC solved the issue. In case libgl1-mesa-dri is upgraded, the file will be restored, so I will be able to check if the upgrade helped. If not, I will just remove it again.