Cannot Edit User Defined Value (FMS)

I have a customer whose previous partner set up several Formatted Searches. However, I'm unable to edit or disable any of them. I know the FMS exists due to the proper icon on the field:

However nothing happens when pressing Shift+F2, or clicking Tools>User-Defined Values. If the focus is on another field that has no FMS icon, Shift+F2 works as expected.

I am able to query the CSHS and OUQR tables to determine what query is being called and can probably alter the query in Query Manager. However, I want to remove the FMS. (Yes, I could theoretically neutralize the FMS by changing the query to a simple select statement, but that doesn't explain why I'm unable to edit the FMS.)

I appreciate any insight.

Randy Davis
Denver, CO