today I solved the above described problem with the forgotten USB stick profiles! It's quite simple:
Every time I'm going to start a new synchronisation I completely clean the stick. I remove the Music and the MediaMonkey directory.
But the file StorageInfo.xml seems to contain the recognition in the tag "storageGuid", isn't it?
I made several tests: If I delete the file, MM creates a new profile. If not, it uses the existing profile...
If this is really the problem, we can close this thread.