This problem is already on General Bug board at:
https://www.photools.com/community/index.php?topic=356.0
I have made another test, this time with some files which have the had categories exported with FP's script. The hierarchical keyword opetion was checked. This time the @keywords have been arranged in hierarchy under 'excluded' nodes and flat keywords without the 'excluded' nodes. BUT, the anomalies remain.
The files, database etc for this test are in dropbox in zip file 'Test 9' at https://www.dropbox.com/s/ic7pkha6vdecd0p/Test7.zip .
I will add this to the report on the General Bug board.