Ok, my colleague figured this out (we're helping each other). Basically, my form has 2 tabs. I worked on the first form and for the second I just copied the first to work on later. And, of course, both had the same ng-form name (the second being the copy of the first). So, that was the problem.

Just to think so much time was wasted!

Thanks a lot for your help - ng-messages can come handy.