Reboot problem

[lucacerone]

Dear all,
lately whenever I try rebooting my machine issuing:

sudo reboot now
the system starts halting but then it get stuck
with the monitor displaying

modem-manager [900]: <info> Caught signal 15, shutting down...
... waiting...
Even waiting for a long time nothing happens and I'm forced to power off
the machine and restart it manually.

Any hints on what's going on? How can I solve this issue?
Should I report it as a bug?

Cheers, -Luca