Comment 24 for bug 194214

Another related bug is this: bug 190934
When I get the key stuck, then unsticking it produces the same broken modifiers. In addition, ctrl-alt-backspace will no longer work -- if you run 'xev' in console and press ctrl-alt-backspace, you get the "Terminate_Server" keysym, which Xorg itself should be grabbing. When that happens, I have to use alt-sysrq-k to kill Xorg instead.