Cause?

Hmm, you're surfing displacement vectors? Or just using them for bounds checking? If it's the former, that's pretty interesting. Maybe try wall smoothing them instead?

If it's just for bounds checking, that doesn't make much sense to me in movement. In a gun, it makes sense to discard that data because it's clearly not the movement choice the enemy's going to make now. But in surfing, you're the one deciding on the exact movement that correlates to the firing angle, which the enemy had already chosen. I don't really see the correlation that says you should ignore the data you collected about that firing angle. But it's pretty late and my brain's pretty fried from refactoring... :-)