Changing time_since_rest doesn't prevent Phantoms from spawning

I'm not sure if this is a bug, but I've got a TimeSinceSleep objective that uses the time_since_rest criteria. If I periodically set TimeSinceSleep back to 0, phantoms will still eventually spawn even though TimeSinceSleep is less than 72000. I understand it's likely phantoms spawn off of some internal variable not accessible in player data. It just seems to me like that would be redundant, and therefore perhaps this is unintended.