Im on 10.8.4 too but I havent had the issue for a few months..
Just recently I decided to redownload an app called iTunesAlarm which wakes your mac and plays music from itunes. I had previously created an automator thingy with the calendar to replace this app but I thought I'd try it again. And since I've had that app the gray background issue reappeard. When going into mission control everything looked weird and the kill dock fixed it again.
So I immediately uninstalled it and without killing the dock the issue went away. So anyone using this app (or maybe something similar like iTaf).. this might be the culprit.. at least it was for me
Hope this helpes anyone
I'm using a MacBook Pro with Mountain Lion 10.8.4 and this issue is still occurring for me. In fact, it seems to be getting more and more frequent. I don't know if it's related to the fact that I use an external monitor at work and then bring the laptop home where I just work off of the laptop screen but there are several issues that I'm dealing with.
Every one of these is sporadic at best. I don't get why Apple hasn't addressed an issue that's been around since 2011 and has spanned 3 different versions of their operating systems.
I solved the problem once and for all!!
I stopped using an external monitor.
It was mostly because my old expensive calibrated IPS monitor was starting to go out and I love using the retina screen on my MacBook Pro. Sometimes I forget that this problem still exists—until I get a notification email about a new comment. It's sad that it's been years without a fix. Mavericks is supposed to have an overhauled multi-display environment, so let's hope that this bug is ironed out in that release. Especially since I want to pick up a new Thunderbolt Display once they're updated later this year alongside the new Mac Pro.