Comment 4 for bug 1043280

I think this is actually the same bug as bug 1037142. The result is just a little different. Test the following:
1. Open a new window (not maximized)
2. Start workspace switcher
3. Click once on the opened, non-maximized window [Workspace switcher closes]
4. Move mouse to the top edge of your screen
5. An orange grid overlay appears covering whole screen [This bug occurs]

6. Start workspace switcher again
7. Click again once on the opened, non-maximized window [Workspace switcher closes]
8. Move mouse pointer to left edge of your screen [Bug 1037142 occurs]

So basically the problem is the same: grid thinks you're dragging a window and when you hit the edge, the orange overlay appears (like when you really drag a window) showing you what's going to happen to the window when you release your mouse. Grid just doesn't know that the window you're supposedly dragging is just a bogus state left behind by the workspace switcher.