Fast User Switching causes Magic TrackPad connectivity problem

Contemplating a fresh install at this point :-/

Thanks for the idea; I'll keep it in mind.

I ended up doing a reformat/reinstall of Lion, and the problem persists.

I think I noticed the problem occuring more quickly when both my wife and I had 3rd party apps that support gestures opened in our respective accounts. So, for the moment at least, we're going to try to leave Twitter, Reeder and Sparrow closed for a few days and see if the problem seems to take longer to arise or what.

I will continue to post things here as I try them.

So, by trying the turn off TrackPad/remove batteries when this happened, I found (or possibly re-discovered, as I think I recalled this once before) that it's almost as if the TrackPad crashes the entire Bluetooth stack in OS X.

What I mean is that, turning the TrackPad back on under these conditions, OS X reports that it's still connected to the TrackPad (green ball icon next to device), has never lost connectivity and, what's more, if I try to right-click and disconnect the TrackPad, Bluetooth settings will hang for a minute, spinning beachball of death. If I try turning off the Bluetooth Keyboard, it, too, will not reconnect. Turning off/on Bluetooth on the Mac also will not allow the devices to reconnect, disconnect, function, anything.

Simply rebooting causes everything to snap back to normal. Also, if I hadn't mentioned before, this occurs on OS X 10.6.8, 10.7 and 10.7.1.

Okay, some potentially good news:

Under System Preferences > Bluetooth > Advanced > option to Allow Bluetooth devices to wake this computer

This is turned on by default and is apparently a per-user setting, not a global setting, which is where the conflict begins, from what I can tell.

My guess is that, when turned on for all users, like it is by default, when the computer goes to sleep, the bluetooth signal gets screwy, probably stepping over itself, to listen for incoming requests for both users for both keyboard and trackpad. And/or, when a user wakes the computer by pressing one of these devices, the signal tries to relaunch the Bluetooth stack for both users for both devices immediately, again probably stepping over itself, setting up a chain of events that will cause Bluetooth connectivity to fail altogether after a few sleep/wake and/or Fast User Switching cycles.

So, for a couple days now I've been running with this option turned off for one user and on for the other user. So, depending on which user is currently logged into the console, you may have to wake the computer by way of the power button or the keyboard/trackpad. The good news, though, is that it would typically foul up after no more than a day, and it's gone a couple of days thus far without issue.

Here's what I found over the last several weeks of using Lion: if my wife and I both made a point to close iPhoto before walking away from the computer or before the other person Fast-User-Switched over to their profile, the problem seemed to go away. I suspect iPhoto used the discrete/accelerated graphics chip, though I have no idea if that's related. Back in the day, I thought I'd noticed the same thing happening if I left Sparrow or Twitterrific open on my profile before my wife FUS'd over to her profile.

Now, we've upgraded to Mountain Lion, and I'm scared to even experiment just yet, but we've continued to be religous about keeping iPhoto closed. In the coming days and weeks on ML, we'll attempt leaving iPhoto open or maybe turning "allow bluetooth devices to wake this computer" back on and see what happens. Oh how awesome it would be to actually be able to utilize features like that and/or not worry so much about leaving iPhoto or other 3rd party apps up and running before the other user logged in!

I'll keep everyone posted as I learned anything new (in case anyone still cares about this problem).

I have found that Mountan Lion 10.8 seems to have largely fixed these problems for me. My wife and I have ceased worrying about whether iPhoto is left open or not on either of our profiles, and the problem has yet to rear its head.

The next step is to again try enabling "allow bluetooth devices to wake computer" to see if that's now fixed, too.