A319 Captain reported the aircraft rolled back a short distance after parking at the gate. Aircraft was brought to a stop and the parking brake was set.

Narrative

Aircraft stopped at gate. Brake set (Handel position); engines shut down. After a few seconds the ramp crew signaled to set brakes and then I realized we were rolling backwards. I applied brake petal pressure; stopped the aircraft and cycled the parking brake lever. I checked the triple indicator for pressure and everything appeared normal. The ramp crew hooked up a tug and pulled us forward about a foot and the brake was reset without issue. I didn't feel we rolled very much due to the amount of reposition that was required. I checked with the first officer and we both remember seeing pressure on the triple indicator when the initial stop was made. I cycled and tested the brakes and parking brake several more time and all worked normally. I considered it spurious because it as operating normally and did not make a logbook entry. Arriving in ZZZ; the system worked normally. I can't say definitely that the triple indicator was checked upon initial brake set but with engine shutdown and normal flows I am 70% sure it was. It would be helpful if when the ramp crew is going to file a report; they inform the pilots so they can file a report as well. This seemed like a minor incident and due to the slight repositioning; I didn't feel the need to file a report; otherwise I would have written it up in the logbook. I should have know better as I have had issues with this station in the past.