[d2kx]

Mmh sorry, can't confirm. It runs just fine on my slow, old, low-end notebook. It also runs fine with mpv instead of XBMC/Kodi. I disable compositing when my windows/video players are fullscreen (KDE setting), force Vsync and have Triple Buffering (it's called Tear-Free-Desktop in the AMD Catalyst Control Center, but it's just triple buffering) disabled (it's disabled by default though). I can see why it would not work with compositing enabled or triple buffering, but that's something for people to try who have problems...

Some sysinfo/kernel, driver, vainfo:
http://i.imgur.com/DhgcyQc.png

Kodi with Vsync forced:
http://i.imgur.com/vzqVgub.jpg

Kodi playing a 1080p Anime MKV:
http://i.imgur.com/h1HKp86.jpg

#edit:

Wanted to try 14.0 but the stable XBMC PPA has problems with Ubuntu 14.10 Utopic right now, the new 14.0 build depends on libafpclient0 but that is not avaible in the PPA and got removed in the Ubuntu repositories with Ubuntu 14.10. I guess it would work if I used the trusty .deb for this library but honestly don't feel like messing with it now.

#edit2:

ok, the dependency was in the XBMC Unstable PPA, so got 14.0 running. VAAPI was disabled by default as expected. I forced it through the advancedsettings.xml but, as noted by you, it works but freezes after about 1 second or so. Nevermind, back to 13.x and everything is working again. Will try to poke AMD about this.