[Paul in Colorado]

I always keep batteries in my pedals even though I use a power supply. I may be wrong, but it seems that when I have a power supply plugged in, it doesn't cause the batteries to run down even though there's a plug inserted in the input jack. I've had batteries in my pedals for months and the LED lights up brightly when I unplug the PS. I don't know why this would be since there's no switch in the PS jack. ????