So everytime you play a replay you can edit it. Now press P at start so at start frame like 500. If you moved in the replay you go to the next frame or something when you try to edit from start. i tried it in a judo replay and when i pressed edit in the 1000 (first frame) then i landed in the 930 (2nd frame). I just found it out by playing around at toribash also you can save the replay then it automaticly starts again at the 2nd frame but with 1000 Frames. Pretty cool glitch / bug or what ever it is i dont know maybe you wanna fix that.

It should save the full replay, maybe a game developer will explain you why that happens, I recomnend you contacting one.

Well doesnt it happen to you if you try? I mean it could be a cool glitch