Service Tax Dates changed when running the Invoice Generation

I have an Invoice with two Pay Items 001 and 002. These are in the same batch. When I run the Create AR function from the Row Exit, the Service Tax dates go into the F03B11 Edit Line as two different dates, one for each Pay Item. When the End Document Processing runs, the records appear in the F03B11 but the Service Tax Dates are both the same date.

I'm not sure why or where the Service Tax Date gets changed.