I opened a support ticket on this and really pressed them for an answer. Their response was that it is not a bug; it's just how Fusion 5 works and that it's a great feature. 
Fusion 4 used to let you unmap the CMD to Start Menu; if you upgrade from v4 > v5, that option still shows in the Key Mappings preferences, but it's a 'ghost' from the old preferences (hence my support call).
Simon's fix is a good workaround, but I just wish VMware would add an option to disable the mapping ... seems rather simple.