Some purchases can be returned. In these cases, the commission is extended and if the item is returned, the commission is removed. There can be other reasons too.
It's not unusual for an advertiser to extend transactions. Lots of reasons such as their budget is short, extended to cover returns, and many just do it automatically nearly every month. So it's not unusual. Though in some cases like the mortgage lenders from many months ago were doing it just to cheat the publishers as several extended, and then failed to pay and closed up shop on CJ leaving many without any compensation.
As I mentioned in another thread, 99% of extensions are for merchants to wait until the end of their returns period. It is usually NOT for fraud or anything bad.