Just a note: it's critical to remember that Kannaduki becomes a spear in bankai.

First, I'll address the bending-reality point. The second ability of the bankai is to change its own reality, enabling it to change form and the path it takes. It ranges from making it longer/shorter to being able to tun corners and shit like that.

The reason it does this is to accommodate the first ability, which I to reverse causality. Put simply, when you drop something, it hits the ground. It hitting the ground is a result of you dropping it. Reversing causality would make it so that you drop it as a result of it hitting the ground—you're dropping it to prove that it really did hit the ground. It's a situation of "A happened so B was the result" being turned around to "B was the result so A must have happened". For any onlookers, it'll look completely normal, because what "happens" is that the spear takes a path that isn't countered.

Now let's expand on that and say that there's a magic shield in the way. Kannaduki won't avoid it, instead hitting it right on, because it doesn't recognize it as truly existing (because magic is like, special). You'd have to break through the magic with the attack, and if you can't do that, then you just your attack blocked.