If you do, the boulder might change direction, and that messes up the mechnaic of the labyrinth.
Especialy be cautious if you walk behind a boulder.

I'm not 100% sure if that's a bug, because there are cases when changing a boulder's direction is really useful.

There is no indicator this should be a feature, and bumping into boulders can literaly softlock your game.
Bumping into boulders should cause damage, but when you come from behind this is prevented. You should simply not be able to pass forward, indicated by the many spell-projectiles which work the same way as boulders, but they are not "solid" by game-terms, so that's why you never experince this with them - definitely a bug on the boulders.