Website iLounge found that there are two errors related to billing coming from Apple's free bumper program.
The first error lets anyone who previously bought their case to get their refund. In addition to the refund, the iPhone owner is still eligible for a free case, effectively giving them two iPhone 4 cases for free.
There is a second issue that iLounge reports that allowed for a single person to order multiple cases and their refunds. This while still being eligible for their free case. They say that one of their editors has already received their credits for three cases. However, they remain unsure whether this is because Apple is not cross-checking the Apple IDs associated with the free bumper orders with those that are simply looking to be reimbursed for a past purchase of multiple bumpers or if Apple is simply handing them out to win some points with consumers.
Apple has not yet commented on the matter.