Originally Posted by KhalilSheikh

Vary each transaction that is linked to the same airline from the same restaurant on the same day by a penny, and you'll be fine 99% of the time. When the airline sees the multiple transactions identical in amount and in the same day/restaurant, it appears as if Rewards Network made a mistake by posting multiple identical transactions.
I purchased 4X $20 gift cards at the same place (each transaction just minutes apart), but charged them at $20, $19.99, $19.98, $19.97 (the difference I paid cash in pennies). They all posted with no problems.