It seems similar on my NTSC 128. Playing with it a bit, I think what's happening is that I'm teleporting then trying to move left or right but still have the stick down slightly. That triggers another teleport while I'm moving. Maybe waiting for the down direction to be released before triggering it again would help me. I'm guessing going left or right is resetting the down detection.
Or I could just "git gud" ;)
Another interesting thing that happened on my 128 is that the background sound would stop for long stretches during a level and then come back occasionally. The actual sound effects (jumping, triggering pads, etc) always sounded properly. I went back and tried to reproduce this but was unable to, so maybe my machine/SID just needed to warm up.
Thanks again for the game. Please, don't feel any obligation to change anything based on my feedback!