<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by LoneStarMike:
I would double check with your credit card company regarding the interest. I know if you dispute a charge you do not have to pay the amount in question while they are investigating. I would assume (hope?) you wouldn't have to pay the interest especially if the charge was ultimately reversed.</font>
But, when you get a ticket refunded (or get a credit from any merchant for that matter), the original charge doesn't get "reversed" - instead, a separate credit transaction is issued. There's really no relation between the two transactions as far as the credit card company is concerned.
The only time a purchase truely gets "reversed" is when a chargeback is done.
A merchant can cancel a transaction shortly after it is made (specifically, before the batch is closed, which usually occurs at the end of the day, although this may be more frequent for a large merchant), but in this situation the charge is never posted to your account in the first place (although your available credit may be reduced until such time that your card issuer realizes the charge is never going to come through). This procedure is usually used in the case where a charge is made in error, or for the wrong amount, and the mistake is realized shortly thereafter, and not for refunds.