Some players may have been charged full price for Alicorn or any of the Thanksgiving animals during the 25% off sale.
We just implemented a fix to prevent this from happening with future purchases during the sale. Also, we have credited the difference in Gems back to players that didn't receive the 25% discount. You may need to restart the game for the changes to be reflected.
Thanks again everyone for letting us know about this issue so we can correct it for everyone!