The crust is drying and stiffening. Then the inside keeps expanding until the crust can't hold in the pressure any more. Poof! The crust pops open and you get the partial ear pictured. I'd call it a good thing because your dough is rising while baking. In order to have a bit more control of it try scoring it in various ways.
Oh that makes some sense. I never thought about how the high humidity stops the crust from drying out but it makes sense. Ohh that's probably why people who bake in dutch ovens have to open the pot towards the end of the bake. So the crust can dry out and harden!