@PlasticAnimal: It's pretty hard to say what is going on there. Generally any effect that changes noticeably over time is to be avoided. Safe effects will be the same no matter what. Some effects will change as the battery dies, but other than that be careful of changing effects.
Something I like to do is use a current meter on the power supply. Then when I hook up potentially dangerous bends like the one you're talking about I can see if it pulls lots of power. If it does, then it's no good.