Haha I had this same thing. The fans in both washrooms are likely connected, they are in mine. Meaning that if you turn the fan swtich on in one bathroom the fan actually goes on in both. So the reason your switch keeps reversing is probably because you are turning the switch on/off in the other bothroom as well. It took me a while to figure this out. I actually took the switch out and flipped it, and then it got reversed again and I wa like WTF, and then it downed on me that maybe they are connected, and they were. I actually put this in my Tarrion warranty 30 day form but I'm not sure if this is a legit complaint.
Anybody else that has 2 washrooms have their fans connected too?