Maybe give Microsoft's customer support a shout. I've heard of a case where the rebuild says it succeeded but didn't, not sure why that could happen. Calling CSS will be a lot faster than getting free assistance here.
It isn't maybe a case where master is somewhere other than the default location and the rebuild put the new files in the default location?
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability