high speed stall/snap is going on....even the best 3D planes will experience this with the exception of foamies and super light electrics


next time try doing a move called the wall make sure you have max elevator(3d rate 45 or more degrees)
fly level at about quarter throttle chop the throttle and apply full elevator.. if you arent fast enough and/or dont have enough elev. throw the plane WILL snap roll.

there are moves where too much elevator will cause a snap too.... such as when doing a loop or an immelman turn... it usually happens at the top of the immelman or the loop