makes me wonder ...off topic-a dude i know customized his power supply for cry baby to 8,4 v. he says he likes the sound of "old battery" on his wah,rather then,as he described,"clicaty-clack" of the constant 9v power supply....go figure...
I don't know the circuit. But if there is a polarity protection diode and if it's blown you can have this problem. If it's the case replacing the diode will fix the problem.