Similar experience: I just bought two separate tickets, using 3x$50 gift cards in both cases.

For the first ticket, the "Your Flight Receipt" email lists only a single gift card under the heading "ECREDITS APPLIED -- eCredits Number 006xxxxxxxxxx"; however the numbers all add up:



So even though only one gift card is listed, the ticket calculation treated the 3 of them as a single $150 voucher with a fare difference of $49.07 vs. the base fare of $199.07, plus taxes and fees, and my credit card has a pending charge of $78.20.

However, similar to the OP, if I pull up this itinerary under My Trips and click on View Receipt, the display there makes it seem like only one gift card was applied and an extra $100 was charged to my card.

However*2, given that the pending charge amount is correct, I am pretty confident this is merely a display glitch.

The second ticket I booked, also using 3x$50 gift cards, has exactly the same quirks (although the original total fare was $318.20 instead of $228.20 so all the numbers are correspondingly higher).

And, footnote: from a software developer/QA standpoint this would strongly imply that the "Total Charged" field in the email is directly tied to the credit card processing system, whereas the field under "View Receipt" that reads "Paid With Visa ending in xxxx" is computed by subtracting the (incorrect) gift card amount from the total fare)