Originally filed as a Mumble bug on Ubuntu launchpad:
"After updating to Natty from Maverick, push to talk no longer works. I've checked the settings and they are correct."
but as it turns out, even running 'xinput test' doesn't show anything ('test-xi2' obviously works), so it looks like XI1 got broken at some point. Xserver 1.9 works, since that's what was used before 1.10rc1 was uploaded to the devel series on Jan 31th.
Author: Peter Hutterer <email@example.com>
Date: Mon Feb 21 15:32:57 2011 +1000
dix: a valuator number of 0 is valid (#34510)