I apologize in advance if someone else has already posted this problem, but I've searched and searched and found nothing on it. It's a hard one to describe, so bear with me.

Basically, since installing Lion (currently 10.7.4) on my home iMac, I've been unable to have windows for more than one application appear at one time. For the most part, applications run just fine. But say I have Adobe Illustrator open and want to drag an image from a folder in Finder into my document. The second I select Finder from the Dock, Illustrator disappears. Click back on Illustrator from the dock, and it reappears, but now my Finder window has gone AWOL. Seems like it's all still there, just becomes invisible. At no time will it display more than one application. Two windows of the same application? No problem. But any time I switch between apps, it shows only the most recently selected app, regardless of what's actually running on my machine. Makes dragging and dropping from one app to another damn-near impossible.

I've read about problems regarding apps becoming invisible, but virtually all posts say they also become unresponsive (ie. don't come back at all when reselected from the Dock), and that quitting and restarting the app generally fixes the problem. This isn't the case for me. Quitting and restarting does nothing. Even a fresh install of Lion did nothing. I find it hard to imagine this could be a hardware issue though. My iMac works perfectly otherwise, and this behaviour is just bizarre. Consequently, I haven't ruled out the possibility of demonic possesion, but I figured if anyone can help solve this riddle, it's all you lovely people.

As for my current settings, I have no desktops/spaces setup (aside from the one), and have turned off all associated features for Mission Control in the System Preferences – more out of an attempt to simplify in the hopes that it would help than out of any dislike for the features. The iMac itself is a 20-inch, early 2008 with 2.4 GHz Core 2 Duo and 4 GB SDRAM.

Really don't know where else to turn. I've got my finger crossed that the problem will fade into memory once Mountain Lion is released, but that leaves me high and dry until then (which sucks the big one). Any help would result in my undying gratitude! Heck, help me solve this and I'll mail you a beer!

i'm not sure this is the solution to your problem, but i'm wondering if it's the full screen mode that causing the problem?

there is a button in the top right corner of apps that support lion's full screen mode. click it and it will go back and forth between full screen and regular mode.

although i don't think illustrator supports full screen mode - at least not Lions. Adobe has their own full screen mode(s) that are accessed by pressing the 'f' key. perhaps something to play around with.

Thanks for the quick response i-rui. Unfortunately, it seems to be more complicated than that. The full screen feature (for those apps that support it) works fine, since the apps become their own desktop and I can simply switch with Command + directional arrows. And you're right about Illustrator not supporting it (was hoping they'd integrate that into CS6, but alas).

Illustrator is just one of the many apps giving me issues. Truth be told, the problem occurs with every single app – Mail, Finder, MS Word, Text Edit... even System Preferences and Disk Utility. If it simply created a new desktop/space for each app, I could almost wrap my head around that, but instead the apps just flicker in and out of existence in a single desktop/space, never able to coexist.

Maybe one of your option/alt key is stuck? That would produce this behavior.

Thanks for the response MX-V. Turns out "single application mode" got turned on somehow. Have no idea how to turn it on (or to turn it off natively), but there's a free app that did the trick for me.

Below is the solution someone was kind enough to post for me on the Apple Support Forums (in case someone else stumbles across this thread with the same questions driving them to sleeplessness). Thanks to everyone for your help!


That sounds like somehow the Single Application Mode has been turned on. I don't know the Terminal command to turn it off, but the free 3rd-party application TinkerTool has it.

For some reason, it's on the Dock page:
https://discussions.apple.com/servlet/JiveServlet/showImage/2-18512864-120259/Screen+Shot+2012-05-29+at+6.43.29+PM.png

If it's checked, remove it.
If it's not checked, check it, Relaunch, then remove the check.

Does any one else have this problem with Lion?

I drag and drop files between applications all the time, I can't imagine this being a general problem with Lion.

I currently only have one Mac running Lion and that Mac is currently in Berlin. If the person using it had this issue I'm sure I would have heard about it.

I'm pretty sure this is a feature... or at least, something that can be enabled. "Single Application Mode".

This fellow says (http://forums.macrumors.com/showthread.php?t=1221589) Quicksilver was the problem -it has a preference that turns this on / off.