Duplicate files: Duplicates, Copies (binary identical)

[Aubrey]

I understand that when searching database for "duplicate" files that
Search -> Duplicates is less rigorous than Search -> Copies (binary identical)

I have a file where a duplicate is NOT found when I use "Duplicates", but if I search same file using "copies (binary identical)" then a match is found. 

Strange?

Aubrey.

[Mario]

Force a rescan of both files. If the problem persists, send me the files.

[Aubrey]

Force rescan solved it.
Why didn't I think of doing that? 

Thanks.