I recently upgraded my Kubuntu 12.10 to 13.04 using the standard upgrade system.

Since then, the computer almost always fails to switch off properly. The screen gets dark, but the computer is still on; alternatively, it is blocked on a terminal-like screen, saying "system will now halt" or something similar.
This did not happen before.

Am I the only one in this situation? Is there anything I can do?

Kubuntu 13.04 64 bits
MacBook Pro 6.2
2.66GHz Intel Core I7
4GB 1066MHz DDR3 SDRM - 2x2GB
500GB Serial ATA Drive @ 7200

Thank you