There was a glitch in the previous version of OS X where the launchpad (iOS style rapid launcher which is genuinely useful for launching apps by typing a couple of letters of the name rather than trawling through the Applications folder or wherever you've put them).
I constantly had an issue where icons from the launcher would get "stuck" permanently on the screen over the top of every bomb else. The only way to reset it was to use the terminal and KILL the Dock process or log out and reset everything.
That bug persisted trough multiple versions of OS X and I definitely reported it,
Biting the hand that feeds IT
