Subject Setting FieldsIndex.Commatext

I have a Problem with 4.2.Ef in D5E.
When I set Fieldsindex.Commatext with for example only one Fieldname
of the TIB_Query, it does not do what I want. The Routine
TIB_Statement.UpdateIndex is called three times, the first with my
FieldsIndex, the second and third time with the query's full field
What do I make wrong?

Thank You Dieter Tremel