There are a couple of items in the MultiBit Help Support section :
+ I sent some bitcoin to MultiBit but they never arrived.
+ I sent some bitcoin from MultiBit but they are stuck
They don't exactly match your problem description but if you work through the steps/ tips systematically you'll get your wallet to match what is on the blockchain.
Also make sure you backup your wallet if you have not done so already.
Backed it up a couple times, and fixed it.
Thanks
!
Love the client.