It's by design. Thats something to do with the 8.3 naming convention. From memory the command strip the long file name extension to 3 to make the match after. I lost my documentation about that, but I found you a older document that told that too;
Use wildcard characters such as the asterisk ( * ) and question mark (
? ) carefully in conjunction with the del and
copy command-line commands. Windows 2000 searches both long and short file names for matches to the wildcard character combination you specify, which can cause additional files to be deleted or copied.
MCP | MCTS 70-236: Exchange Server 2007, Configuring
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