Open Radar

 
Summary:
Under particular (but fairly common) conditions, dragging a window to another desktop will not work.

Steps to Reproduce:
- Invoke Misson Control on a desktop with two (or more) applications with windows present, at least one of which only has a single visible window.
- Drag any window up to the row of desktops at the top of the screen (do not release). Note how applicable desktops are highlighted when you hover over them.
- Drag the window back down into the current working desktop and release the mouse button.
- Repeat the last two steps with any window belonging to an application with only one visible window on the current desktop.

Expected Results:
The other desktops to act as drop targets.

Actual Results:
No such drop targets, and no visual indication of a potential drop spot.

Notes:
The behaviour gets weirder from there. Repeating the same action with the same window appears to cause regular alternation between working and not working, but switching windows seems to ensure it won't work every time.

Step three isn't strictly necessary, but it gives you more windows to test the behaviour with once it has started.

I think this is new in 10.8.1; I've only caught myself having to drag things twice recently. The only other Mac I have access to is running Lion and this is not reproducible there.

I have Mission Control set up to group windows by application.