Why does spaces keep capturing keyboard input some times after switching spaces?

I'm running snow leopard on a fairly new macbook pro 13" (september 2010).

Sometimes the black visualization showing the available spaces and the space I'm currently on doesn't disappear when I have switched between two spaces. When this happens, spaces seems to steals keyboard input from the application(s) on the space I have switched to. Sometimes the visualization disappears after I keep switch spaces some more, but sometimes I have to force a reboot.

Also, spaces seems quite slow at times.

Does anybody else experience the same thing, and is there anything to be done about it?

I find that killing the Dock only sometimes makes the problem go away. Usually keyboard input returns, but if I switch spaces using the keyboard shortcuts, the visualisation sticks around & keyboard input is stolen again.

What I have found to work is putting the display to sleep. I've had the bottom right corner of the screen set to do that for ages, so it's quite convenient for me. I've never had this method fail; once the screen is awoken, the problem is gone & doesn't return when I switch spaces again.

To me this suggests that the problem isn't actually in Dock, it's in the system's EventTap subsystem, the bit that lets stuff like Spaces, Screen Sharing, LaunchBar, & Spotlight take keystrokes before the focussed application gets them. I've actually experienced a similar problem with Screen Sharing, where the system whose screen is being shared gets its keyboard input mangled if a modifier key is pressed on the viewing computer & not released until Screen Sharing has lost focus. It's sort of the reverse problem, but it indicates that perhaps the Spaces problem is the EventTap framework getting stuck in a similar way, never sending the message that Control isn't being held down any more.

I experience the same issue on a regular basis. Pressing CMD+W right after noticing that the spaces window will persist makes the window disappear most times.

If it doesn't, you can kill Dock from Activity Monitor (start it from the Applications folder in your Dock, select 'Dock' and click 'End Process' or the like). This always makes keyboard input work again, but the issue will reappear very soon.

If I could, I also would give bounty for this!

/Update: The Mac OS X 10.6.5 changelog suggests that this issue will be fixed in that version: