Bug#508589: I also encounter this bug regularly
I'm using an up to date Lenny installation, standard kernel:
Linux version 2.6.26-2-686 (Debian 2.6.26-21lenny4) (email@example.com) (gcc version 4.1.3 20080704 (prerelease) (Debian 4.1.2-25)) #1 SMP Tue Mar 9 17:35:51 UTC 2010
I encounter this problem much too often and each time
it requires a hard reboot. Strangely, the mouse still works so I can
log out of kde, but then the shutdown process hangs until I hit
CTRL-ALT-DEL. Then it continues, but the laptop (Dell 8600) doesn't
shut down all the way. I have to hold the power button for 10 seconds
and then it does shut down. This is a very low level issue.
I don't use kppp. This happens with regular poff. I suspect
it's related to the cdc_acm driver which is the one being used by my
phone (motorola e815) through a usb cable. It's not 100% repeatable.
It might be a race condition and I have encountered it most often a
couple of seconds after issuing a poff, before disconnecting the usb
cable. It does not seem to happen if the ppp connection is terminated
by the other side (LCP terminated by peer).