Do I assume correctly: Fingerprinting is done for all objects in digiKam. Selecting a specific album when searching for duplicates finds duplicates in the whole DB for objects in that album, NOT only duplicates just within the album.
To be more clear: The DB contains objects A, B, C, D, D2 (which is a duplicate of D). Album Foo contains B2 (which is a duplicate of B), E, F, F2 (which is a duplicate of F).
When limiting the duplicate search to album Foo, I get B2 and F2 reported as dups, not just F2.