I suppose I should start with a rant on how XMonad sucks to get everyone's attention. However, truth is I've been enjoying xmonad for some c. 5 years now, without any problems whatsoever. However: 

I've recently upgraded my Ubuntu from 10.04 to 14.04.

Xmonad appeared to work after changing the syntax of dmenu_run and recompiling.

However, sometimes when switching workspaces, I end up with with some garbage window with the following properties:

* slightly offset to the bottom & right from the normal location (slightly means: a couple of pixels)

* the area usually contains the contents of the window that was displaying right before making the switch (but as I set, slightly offset to the right & bottom)

* usually the window is killable using my standard kill-key-combo.

* It appears (though I'm not sure) that google-chrome if often involved in this. One observed behavior: after killing the "ghost window" everything seemed to work fine again, except that chrome was gone. Tentative conclusion: the ghost window was in fact chrome.

* My "unfloat" modifier (Mod-T) doesn't change anything

When observing the above, I just run windows full screen and use various workspaces for the various windows.

* A behavior that appears related: in a few cases I did not manage to get rid of the ghost window. In those cases I got some kind of mosaic inside the full-screen chrome window, comprised of ca. 5 times 5 smaller, mirrored rectangles which contained part of chrome. I'll try to make a screenshot next time this happens.

I'm sorry if the problem description is somewhat vague, and/or if I'm not using the correct terminology.

As I said, I've set up XMonad years ago, and haven't changed a thing since so I'm somewhat lost for the right words at times (the correct terminology is in my fingers)

Any pointers to debugging this problem or requests for specifc configs/logs are welcome.

regards,

Klaas