Computer shutdowns on starting from hibernation

[Óscar Fuentes]

Since a batch of upates installed three days 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. 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.

I'm on Kubuntu 13.04 AMD64.