Still the same with kernel 3.11.0. Tried with VM=0, aspm=0, disconnected my UPC
(just in case it was something with a "battery" state or something similar),
tried Gnome 3 and XFCE, all the same. The only thing working for now is to set
dpm=0 or to force ret=1 in ni_dpm_set_power_state when checking what
ni_restrict_performance_levels_before_switch answered.

However, I don't know if the problem is with ni_dpm_set_power_state or with
something executed after, so I'll play in there.