Created attachment 111292 [details]
Youtube video depicting the artefacts.

This is what I get if I run any kernel newer than 3.14:
https://www.youtube.com/watch?v=nx2-Fvihzxg
Those artefacts appear as soon as new kernel is selected in GRUB, and remain
after logging into X session.

The last kernel working without artefacts is v3.15-rc2-trusty for Ubuntu, and
3.14.7 for Arch. All later kernels have those artefacts.

I updated mesa and xorg to those form ppaibaf/graphics-drivers ppa on Ubuntu,
and on using git version on Arch but it did not change a thing. This regression
is solely kernel-related.

GPU: Mobility Radeon HD 3200 (RS780M)
System tested: Arch, Ubuntu 14.04, 14.10
Kernels affected: 3.15 and onwards (tested up to 3.19-rc1)