Did you check to see if the UDF is being sourced from another object?
Also, it might be worth opening both the compiled header and detail _bus.vbs files in notepad and search them for the field being manipulated by the script. There is a chance it is happening in another script file that you might not be aware of, if you do find it in the SetValue method's first parameter, scroll up until you see the first line beginning with Sub, then take note of what follows after, that is the event it is being triggered under.