Ticket Exchange

I'm having a little trouble figuring out a ticket exchange and how the price maps break down on our batch reporting.

For our ticket prices we break down everything at the price map level, so for each price type we have six price maps applied for items such as base price, GST, fees, etc. 

For this particular exchange it was an upgrade in price of $18, which should have been applied to just the base price and GST price maps (which happens for every other exchange we have done so far this year) For this particular exchange, however, Tessitura has pulled the $18 amount from four of the six price maps at random dollar amounts. I haven't seen this before and can't quite explain it to our finance people.

Does anyone know what the exchange process is in Tessitura in regard to price maps? Has anyone who uses multiple price maps per price type encountered this?