Officially weird
For completeness (and because I'm stuck for ideas), can you post the results of a RESTORE FILELISTONLY on both backups, as well as the output of a SELECT * FROM sys.database_files on the source database?
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