Failing steal negates a successful thief waylay. In that if you have someone distracted due to waylaying them and you steal from them they stay lagged. If you steal and get the 'Oops.' fail message which causes your target to yell out any of the failed steal yells then they're no longer lagged. This happened to me about four times already and I'm starting to think it may be a bug or an unintended side-effect of the code. Since I know if someone is lagged by thief waylay they remain that way until the timer wears off or combat is initated against them. And failing a steal does not initiate combat, just causes a yell.

n/t