I had to switch to Pidgin because of this. It's definitely a Miranda problem. I really didnt want to switch but most of my contacts now have switched to facebook. The Facebook messenger itself sucks and while Pidgin isn't as good as Miranda, in my opinion, I haven't been blocked in the last 2-3 months. With Miranda I lost my facebook account even after setting up all their security crap. I named 3 trusted friends to send me codes if I ever got locked out. Even with that, facebook locked it and wouldnt give the account back..
I check these forums every so often hoping those working on Miranda can fix it as I'd prefer to go back to it.