This is a known behavior. I reported it as a bug a while back. Microsoft has supplied a work around. You can enable TraceFlag 272 on your server. There are other workarounds as well. Check out the Connect entry for more information.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning