Comment 24 for bug 189185

I am also able to reproduce this with the ultradock x4. Based on http://alcopop.org/unix/linux/x40/dock/ I tried undocking using the kernel's dock interface:

echo 1 > /sys/devices/platform/dock.0/undock

This did indeed cause the dock light to go off and the monitor to switch back to the thinkpad screen, but then the laptop froze (it did not respond to typing on its keyboard and the second hand of xclock stopped moving), until I plugged it back into the dock, at which point it began working again.

I have attached the relevant lines from /var/log/messages. The most interesting one, occurring immediately after undocking, is:
Jun 4 09:59:52 ergates kernel: [ 1755.335605] ata2: soft resetting link
Jun 4 09:59:54 ergates kernel: [ 1756.965663] ata2: failed to recover some devices, retrying in 5 secs