This is an interesting bug (a bug that twinks might not be so happy we're shedding light on it, but it is a bug nonetheless): apparently Toughness, which is the bonus that comes from the mining profession, is giving a much bigger buff than designed at tier 3 of the ability. Instead of giving a bonus to health (as it's supposed to, and as it does for miners not within the 225-299 range), it's actually giving a bonus to Stamina. So level 19s with mining between 225-299 are actually picking up about 700 health, instead of the designed 70.
Apparently twinkinfo.com has been waiting on a hotfix for this one for a while, but apparently it's not fixed yet, and twinks who have leveled past 300 are a little angry that the lower-leveled miners are picking up a couple hundred more HP (not to mention, you know, the people being killed by the overpowered twinks). Hopefully Blizzard will get this fixed soon -- it seems like an obvious bug and a fairly easy hotfix.