Thanks for the quick response. However, I have not been using "directory mounted" drives, and the hover trick points to the identical filepath for both files of any duplicate set.
I did manage to get a list of affected albums by doing a db extract to xml, then grepping for 'name="Filename"', sort, sort -u and diff. (I love unix/cygwin for this sort of stuff!). There may well be a better way, but that worked for me.
From this I was able to determine that the issue occurred around the time that I was restructuring the data storage so that 'instead of all composers starting with B' being in the same flat directory, I added subdirs such as '...\B\+Beethoven\', '...\B\+Bellini\' etc. I did this from within MC so as to avoid losing db statistics info. However, at that time, I had the actual storage mounted from a network drive, so possibly that may have been the underlying cause. The db itself was still local, though. Even then, not all of the directories moved were affected - maybe only 5% or so. Annoying.
At least now the storage is back on a directly mounted local drive, so I can now plough through those albums identified and clean them up.
Looking forward to MC27.
Best regards