Bruce, if Im not mistaken what we call a snap roll in in the states many others call a flick roll. That being said I have seen this issue many times in the pattern sportsman class. The sportsman sequence has a two consecutive loop maneuver that tends to bite newbie pattern pilots in the butt. Typically new guys to pattern have their controls set way too hot, add in that most R/C pilots set their CG too far forward. The end result is that some guys during that double loop will come into the first loop with plenty of speed but get off the power too much during the backside and get back into the power too late. Then trying to get through the second loop they pull too much elevator and the airplane snaps out of the loop. It's a combination of the three things, change any of them I.E. move CG rearward a smidge, reduce overall elevator throw or fly faster and the airplane stops snapping out of the loop.