Upstairs: I just replaced some halogen track lights with LEDs. The switches were double pole and are illuminated when the lights are off. This caused the LEDs to have a dim light even when they were turned off.
So, I decided to switch out both switches for some non-illuminated double pole switches that I had downstairs. Everything seemed fine, but after switching the breakers back on, two things changed:
One fixture (which shared a panel with one of the downstair switches) switched "direction". I'm almost positive that up used to be on, but now it's off when it's up. As far as I know, this is not a double pole switch.
A downstairs ceiling lamp with a pull switch quit working.
I'm more worried about fixing #2, but thought it was worth mentioning #1 in case it's related.