I wonder if this is the same problem I had with my NIB RIA 1911, which would double-pop. It was so fast I didn't realize it was happening at first. Tracked the problem down to some unpolished parting lines (seams) on the disconnector which interfered with its operation. Polished them down with a Dremel tool and it was fine after that. This was part 33 in the official government manual on the gun.
I guess the original JMB parts were machined, whereas this part was from the newer and "better" RIA stamping-out manufacturing process which left those parting line ridges. They were small, but in a bad spot to leave "unchased" at the factory.
Dunno if that what it was with Tisas' guns, but just relating a possibly related incident. I was never made aware of any recalls from RIA on it, but looking back, I think a couple of magazines of rounds would have worn those ridges down, thus curing the problem naturally.
Of course, it could just be a too-refined sear which is causing it. Releasing the slide with the slide stop results in a double whammy inertia-wise.
Terry, 230RN