Yes it is. First these couldn't be FFCs because those are name restricted, so OP couldn't be using one of their FFC's for another passenger (it would have to be converted to an ETC to release the name restriction on redemption). So we're only dealing with ETCs, which the way the ticketing services are setup only 1 ETC can be still be deducted/applied per ticket issuance transaction. So if you have multiple ETCs being applied the system needs to combine them as a single cert to deduct. The fact that the consumer doesn't realize this is what occurring anymore speaks to the heavy investment UA made in simplifying credit use, but at the end of the day the limitations in the ticketing process wasn't changed - how the credits are applied was.

Ultimately what seems like you choosing multiple credits works as
1) Select multiple credits on payment page
2) System combines credits into one certificate
3) Ticketing deducts value from new credit.

If you want proof this is occurring - in case 1 OP would have had the same PIN code before and after the transaction. In case 2 OP would have had a new PIN code with the remaining value, matching neither of the individual two credits that were used.for the transaction