This has been a most interesting exercise. The keyword 00 Brad is somehow different. It was one of the first keywords I used and it has been used over 6,000 times in the database. The oddness is likely to be in the blank space between 00 Brad and the following comma visible in the screen shot:
As you suggest, I can probably locate all the 6,000 files, add a new unique keyword to them, delete 00 Brad from the database, locate all the files with the new unique keyword and add 00 Brad back to them.
This might clean up a problem in the database, but it will not fix the dropdown list. Deleting a keyword from the database will not remove it from the dropdown list.
Using any keyword other than 00 Brad will move it from its current location on the dropdown list up to the top of the dropdown list. If I add 00 Brad to something, it gets added to the top of the dropdown list, but is not removed from any other location on the dropdown list.
I need to clean up the weird keyword and then find a way to reset the dropdown list. Any suggestions?