Player takes lava damage if crouching on a soul sand block next to lava.

If you are in the nether and you crouch on a soul sand block close to the middle, nothing happens. If you move to the edge of the block while on the soul sand crouching. And the edge of the block you are moving to has lava there. you take lava damage. 

This happened to me in the nether. I crouched on soul sand next to lava and moved toward the lava and took damage.