The reason you're seeing that is because buckets don't empty from reactor heat until 4000 heat. All of those components require cooldown, which is where it's pulling the mk2 from. Try dropping some ice in there and you'll see that it reduces the heat down to almost nothing. That's because ice removes heat as soon as it can (i.e. 300 heat)
Still that would mean a flaw in the planner because when it gets to 4000 heat it wont go any higher thus it can run endless cycles