I'm not sure the title is the best, but it's the best I can come up with right now.
I've been replacing all the outlets and switches in my house, and for the second time found an electrical box with multiple circuits running to it, with the neutrals tied together. Last time I could fix it semi-logically because it was a multi gang box, and I could separate the circuits. This time, I fixed it, but I'm not sure if it's clear what's happening, for someone looking in the future.
From what I can tell, what happened was that the bedrooms used to just have a switched outlet. At some point, they added overhead fans, and tied those to the already existing switches. In this room, the power initially came from circuit 1, to the switch, then to the outlet. When they added the fan, they ran that cable to the outlet, not the switch, and for reasons I'm unsure of, also connected the outlet to circuit 10. Maybe so you could have a switched outlet and an outlet that always got power, not that it was wired that way.
The upshot was that the fan, outlet, and switch were all tied in to both circuit 1 and circuit 10. To fix this, I capped off the wires from circuit 1 in the switch, and cleaned up the wiring in the outlet, so that they're all only being fed from circuit 10, and the switch only controls the fan.
Is there a better way to fix this? I don't want to mix multiple circuits together, which is why I removed circuit 1 entirely, but it means that the wiring for the fan is tied to an outlet it would seem to have no real connection to. Should I leave a little note for a future person, explaining what's going on and that it wasn't my fault?