Situation:
I flush the upstairs toilet. It flushes just fine.
About 3 minutes later, the other toilet downstairs does the end-part of a flush. I can hear the valve downtsairs close(makes a reassuring "thunk" sound).
Did a little experiment. Flushed upstairs toilet, ran downstairs and watched the other toilet. The water level in the tank goes down a bit, and it of course flushes back to normal level.
Any remedy for this?