Suddenly, it seems that when I attempt to move a single keyframe, no matter in what place, two black lines appear next to it. Once I drag it and leave it in a different position (I am in the DopeSheet but happens too with TimeLine) the whole animation gets distorted. That is, what I drew in the first keyframe appears in the last position and the rest also change to an apparent random place.
I am a bit afraid that everything will move from place and I won´t be able to un do it.