Still no solution but an interesting tidbit: I've tried running pm-hibernate from the console with debugging.
This meant that X session was not locked and, now after resuming, the apps are still there and the mouse moves. Thing is, nothing else works: can't click anywhere, alt-tab does nothing, only switching back to console works. Clock is stuck at 20 minutes ago, too.
Also, the mouse pointer occasionally changes shape when I hover above certain spots and weirdly enough it uses the desktop icon.
Any ideas?