Update: As I've noted in my comments to bug 499399, I found a link between this behaviour and the kernel version that I'm running.
Karmic kernel is fine; various versions of 2.6.32 don't work.
Therefore, it may be a different bug.
Update:
As I've noted in my comments to bug 499399, I found a link between this behaviour and the kernel version that I'm running.
Karmic kernel is fine; various versions of 2.6.32 don't work.
Therefore, it may be a different bug.