Since a batch of upates installed a few weeks ago, when the system starts from hibernation, after reading the saved hibernation state, on reaching the point that it switches to graphical mode, the computer powers off. It changes back to text mode and does what looks like a fast, but controlled, Linux shutdown and the computer switches off. When it is started again the system boots normally (i.e. hibernation state lost/ignored.)
I'm at a loss diagnosing this problem. I've looked into system.log, pm-suspend.log, dmesg... without seeing a trace of what happened on the de-hibernation process. I came here looking for advice on how to investigate this. If there is a more appropriate forum, please tell me.
The main suspects on the list of upgraded packages are libdrm, libkms and libc. It also upgraded qt and the kernel, but since the update the problem also happens with the old kernel, so I discarded the kernel as the probable cause.
Suspend to RAM works fine.
I'm on Kubuntu 13.04 AMD64.