I would check the common cable connection on the valve end. It sounds like it may have came loose.
I'm not 100% sure if this is the case because if my hunch is correct you would get a similar results no matter which of the two zones you ran, but it is possible in case you are getting a partial (high impedance) connection to commons.
Basically what I think is going on is that the power applied to zone 2 can't find a low impedance path to the Common terminal and instead bleeds through the zone 1 valve.
I can be wrong. I've never checked if Rachio actively connects inactive zones to the commons. If they do, my theory could hold water...