In some places, they misapply the Limit rule of "half the bet" in NL. There are lots of places that do this without realizing they're wrong and it's sorta become the "norm", so when the original raise was a raise of 1500, the 3K all-in bet raised 900 on top of that, which is more than half of the original raise. In select places (again, incorrectly) they will allow that to reopen the betting.
