Mission Control occasionally freezing computer and garbling screen content
You can do a couple resets to the computer to see if it resolves the issue. 


Disk utility (application) > select 'Macintosh HD' on the left-hand column > and click VERIFY disk under FIRST AID. 


This takes about 2 - 3 minutes and will let you know if you have a corrupt hard drive which might be causing that issue


Reset PRAM -- Shut computer down > hold down: p + r + Command + Option > with these four keys held down, proceed to hold down the 'POWER' key as well in the top-right hand corner of the keyboard. > hold down all 5 keys until you hear TWO sounds come out of the computer. 


It'll be that familiar chime sound that it makes upon starting up normally

These steps work for all Mac computers -- let me know if this works