Sprinting across gaps doesn't fall

When you sprint across a 1-block-wide gap, you sometimes don't fall through but carry on sprinting across the blocks.

What I expected to happen:
I expected to fall down between the blocks.

What actually happened:
Sometimes I fell between the blocks, but I often sprinted across the gap.

Steps to Reproduce:
Start a new world.
Place blocks in a straight line, 1 block apart (block-gap-block-gap-block)
Sprint across the blocks.
Repeat.