There is a philosophy of leading and following (not one I subscribe to, but it exists), where the concept of lead and follow is more blurred. I've heard it described as a dialog, an equal partnership, or other things, where the man proposes (rather than leads) a step, and the women is free to accept or ignore the proposal, and counter with something else, which the man then has to deal with (follow).
I agree with you though, that followers who hijack the lead (whether to change the steps or the rhythm), can be be difficult to deal with. Earlier in my tango development, I always assumed that my lead wasn't clear enough, when things like this happened. Now I'm a little quicker at figuring out that she didn't really care what I lead, and simply wanted to do her own thing.
To be honest, I've only had one really memorable (in a good way) tanda with a follower who did this (and in fact she was so good, that I was anxiously looking forward to what she was going to do next), since her stuff was better than what I was going to lead. Of course, she might have simply been bored to death with what I was doing, in the first place (she was so much better than me, where I wouldn't doubt it).