I have 2 rows of virtual desktops. If a window is placed at the top of a virtual desktop of the second row, moving this window to the left or the right using the keyboard makes it switch between the upper and the lower virtual desktops at each key stoke.
In case the explanation is not clear:
 - hit ctrl+alt+shit+right arrow => window move to top desktop
 - hit ctrl+alt+shit+right arrow again => window comes back to bottom desktop
 - etc
(The window moves to the right as expected.)

This happened after an upgrade to the latest svn.