Ok, it happened a second time with a similar message; this seems to occur
randomly and unpredictibly as always.

It is definitely a UVD-only issue. I've applied the radeon.no_uvd patch some
guy wrote from here: http://pastebin.com/0mRGb224. Now with uvd turned off, 32
out of 32 attempts have been successful. No more hibernate problems, but UVD
doesn't work of course.