Launching .desktop files causes the command to be executed with the path to the .desktop file itself appended. To reproduce: 1. Navigate to "Kate" in the launcher, add it to the Desktop 2. Click on the new "Kate" icon on the desktop 3. Kate opens the .desktop file it was started from This breaks starting most applications, as they don't deal well with a stray argument.
Also have a read of Bug 421364 and discussion under Bug 421329
*** This bug has been marked as a duplicate of bug 421364 ***