Powernow-k7 hang on Acer Aspire 1304XC

I experienced hangs when I used powernow-k7, so I started to experiment.

I found that the computer hangs only when I switch between performance and powersave echoing to scaling_governor, while if I change scaling_max_freq everything works fine.
So if I set powersave and then I turn back to performance, most of the times the computer hangs, but if I am in performance state and I change scaling_max_freq to 665000 kHz and then I change again scaling_max_freq to 1529000 kHz everything works fine (even iterating it)
The cpu speed really changes in both cases (accordingly to /proc/cpuinfo, bogomips, and monitoring time of execution of a small script I wrote).

My experience maybe means something, maybe not.

Hope this helps solving the problem.

David