This one has me baffled.
There is an outdoor receptacle I'm replacing. The top outlet has never worked, but the bottom outlet does work. I took everything out, marked all the cables, replaced the outlet, placed the cables exactly where they were before, and now both top/bottom plugs function; BUT, now there is a nearby light switch that is stuck on the ON position. Flipping the switch inside the house does nothing, the lights stay on.
I put the old receptacle back, and everything is back to normal. I put the new outlet once again back in, with the cables exactly where they were before, and the switch won't turn off, stuck in the ON position for some reason.
I've tested every single outlet in the circuit (that I could find) and they are all 'wired correctly'.