That comment makes a good point but this was no home-rolled RNG. unif(0,1) simply came back less than 0.4 a few hundred times in a row, or the Random Number God

That comment makes a good point but this was no home-rolled RNG. unif(0,1) simply came back less than 0.4 a few hundred times in a row, or the Random Number God demanded sacrifice and was propitiated (the client fired us and the RNG has behaved ever since).