Just got home and had a better check of the situation.
About 6000 files have a heavily corrupted "Genre" column.
Files in the Dr.Who series's, files with no series and files with other (than Dr.Who) series's. Files I certainly did not touch, not select....
60% to 70% of the library.
I am renaming through the Genre in the tag browser so fixing it is quicker than through meta data editing
Then I am going to try changing the column definition to straight text and hope the problem goes away
