If a player holds A and D (for example) while moving along an edge of blocks and facing the blocks, they will move slower than if they pressed A normally. While this behavior appearing does make sense in the context of the movement normalization fix, I am unsure whether it is intended as the backward movement should have minimal effect on the sideways movement here.
You still get the full normalized motion, but since you're against the block edge, the sideways part is zero'd out, leaving only part of the full motion.
This is the same for walking against a block.