From the description, it takes advantage of belts being a little weird, but if it actually hits 100% that setup locks up.

Also, as pointed out, that setup can be made more reliable and not-glitch-using by making the bottom left corner of the loop a slower belt.

I'm running several similar setups without any hiccups. It's a three year old post, possibly the behavior has been slightly adapted.

Oh and if you're hitting 100% you're using too little nuclear power or building not enough nuclear bombs ;)