Strange collisions at the edges of boxCollider2D

Hi folks, first things first, sorry for my english..

I'm trying to figure out how to fix a bug in my breakout game and maybe someone can help me..

Components:

• ball - CircleCollider2D, 0 friction and 1 bounciness

• block - BoxCollider2D, 0 friction and 0 bounciness

Sometimes, when by ball hit the corner of a block, she take strange and unpredictable directions.. how can i do to avoid this? i've tried to switch the boxcollider of my blocks with a poligonal collider, with 45°-smooth enges, but nothing changes..