When I walk on the edge of soul sand, my movement speed is as if I'm not on soul sand. It wasn't like this before the Nether Update, I believe.
This also happens with ice—when you walk on the edge, it's not slippery.

Steps to Reproduce:
1. Go to the Nether (optional);
2. Find or place some soul sand;
3. Walk on the very edge of it.
Observed Results:
I move at normal walking speed when I am at the very edge of the block.
Expected Results:
I should move at the same speed regardless of my position on the soul sand.

Video is available here. Pardon the resource pack.