Not sure exactly what you're referring to (didn't find "m1" or "m2" anywhere in the paper), but ...
When a monstar leaves the counter (due to a SUB lever emitting a bunny), the monstar has to proceed to the area under the ladder, where Tim has to kill it in order to proceed.
If Tim pulls a SUB lever when the counter equals zero (no monstars), then the bunny will die on the ceiling spikes and be removed. Tim will not be able to reach the ladder and will have to exit the branch point and proceed to the next spot.
When a monstar leaves the counter (due to a SUB lever emitting a bunny), the monstar has to proceed to the area under the ladder, where Tim has to kill it in order to proceed.
If Tim pulls a SUB lever when the counter equals zero (no monstars), then the bunny will die on the ceiling spikes and be removed. Tim will not be able to reach the ladder and will have to exit the branch point and proceed to the next spot.