Comment 4 for bug 801106

Affects me as well, couldn't yet determine the cause either. It seems as if it sometimes locks itself while normal use.
I have to note though that sometimes other keys lock up as well, namely Alt or the arrow keys. However those can be unlocked by double-tapping the problematic key. But not for the Fn lock, I've tried many combinations without success.

Hibernating is a workaround all right, but it's much slower than a reboot, which makes it a poor option.

Machine's a E420s, with 11.10 amd64

Uname: Linux 3.0.0-14-generic #23-Ubuntu SMP x86_64