I've seen this bug for a while, but I thought I'd finally post it because it has started to really annoy me. Enable spaces and force Parallels into a particular space in the Spaces preferences. Make sure the Windows taskbar is located on the bottom of the screen and the OS X dock is on either side (not sure if this is required). In any other space, open a pop-up list that happens to extend beyond the bottom of the screen. This includes lists in any apps or from folders in the dock (I have my apps, utilities, and documents folders all available there). Move the cursor to the bottom of the screen to where the arrow is to extend the long list. Spaces auto-pops over to Parallels all the time. It is, of course, possible that this is a Spaces bug since, in my opinion, Spaces should *never* switch to a different space without some sort of user interaction (app change or keyboard shortcut), but I think it has something to do with the Windows taskbar being at the bottom of the screen in all spaces. Steve
I don't think it matters whether it's in Coherence or not, though that's the mode I'm usually in. Also, I've just noticed that it does not happen all the time, which of course, makes it harder to reproduce. But sometimes, like earlier this morning, I can get it to happen constantly. Steve
Cannot reproduce problem May be you are using Warp? http://www.simplehelp.net/2008/04/14/how-to-use-your-mouse-to-switch-between-spaces-in-os-x/
