Check attached screenshot first - it's hard to describe it. In this example xsensors is affected with "Icon=/usr/share/pixmaps/xsensors/default.xpm" line in .desktop file Desktop files using just name of the icon eg. "Icon=bitcoin80" (which is still XPM file) works fine
Created attachment 4649 Screenshot
*** This bug has been marked as a duplicate of bug 9221 ***