I'm having the same problem. X is constantly crashing (as in, the screen freezes and takes no keyboard or mouse input), and the last time it crashed and I restarted, I found that the "switch applications" setting had been disabled. I opened up "System settings" -> "Keyboard" and set it again to "alt-tab" and now it's working again. This is the first time this particular bug has happened to me.
I'm having the same problem. X is constantly crashing (as in, the screen freezes and takes no keyboard or mouse input), and the last time it crashed and I restarted, I found that the "switch applications" setting had been disabled. I opened up "System settings" -> "Keyboard" and set it again to "alt-tab" and now it's working again. This is the first time this particular bug has happened to me.