There are a couple of wonky things with the threat system yeah, such as some stuff like Eye for an Eye sometimes pulling enough hate that it'll at least get one or two mobs on you after even two Flashes or Overpowers, or Twinania dragons flying straight towards someone who didn't move or touch anything at all based on something silly like their first name. Most buffs seem to pull more hate than they probably should for no apparent reason, Regen I'd say I'm on the fence but I agree it shouldn't pull that much to instantly get everything on the healer between pulls, at least it should get everything to yellow or even orange, if anything increase the hate its original cast produces and maybe what the ticks do too though this is really mostly only an issue in dungeons with closer mob packs.