Just found this thread and thought I might share this.

On June 16 I booked two separate reservations on united.com for around $3.3k each for Sep. Different people, dates, and flights. I realized I used the wrong credit card so I booked another two for the same people, flights, and dates, and then went on to cancel the original pair. All within 24h hours of the original booking of course. Got the refund emails promptly but no actual credit card refund. Called back June 29. Agent said the problem is the cancelled/active reservation pairs had something in common that prevented the refund but I don't remember her exact words. All 4 eticket numbers are different. And the cancellation went far enough that I managed to reserve the same seats later on the new res. Whatever she did, both cancelled reservations now show as Refunded on united.com. Don't think I saw this before calling. I am still waiting for the money though from what I read here this is within normal.

Any advice what is going on here? Is it better practice to cancel first and then rebook? I was not worried about finding availability on the rebook. Largely went down the rebook-first-then-cancel route because I was curious and I saw that recommended somewhere.