(IGNORE THIS POST: Problem apparently gone) This one seems a mystery. Went to one of my empty rental properties where I was unaware of any previous problem, and noticed some lights not working. Tenant had turned one breaker off. I turned it on and that breaker controlled two 3 way switches in different rooms that control parallel lights on back patio. There's also a pigtail on what may be the feed (didn't test yet) which likely goes to a single pole in the same room as one of the two 3-ways (or perhaps a receptacle also). Problem is, with breaker on, patio lights stay on all the time no matter what combination is made with the switches (i.e., on, on, on, on). Had to turn breaker back off and haven't gone back to diagnose yet (travelers SEEM to be wired OK at quick glance), but is there an obvious solution here??? UPDATE: For no apparent reason, everything is now working properly. Tenant must have come back to do something, but it wasn't obvious. Anybody ever seeing an on/on/on/on condition is still welcome to reply.