Shift walking on Soul sand/Path Block/ Farmland makes character catch fire when by lava

Was trying to build a bridge across to an island in the nether, started on soul sand- Shifted to place the block, caught fire and couldn't place the block down- Minecraft acted like I was in the lava while trying to place the block. Wondered if it was with other blocks- tried Path block, farmland- same effect.

What I expected to happen:
Expected to build bridge with nether rack, couldn't build bridge W/O moving to creative as lava was three deep

What actually happened:
Blocks wouldn't place, character caught on fire

To reproduce:
1. Place Soul sand, Path block, or Farmland by lava
2. Shift and try to walk to edge of block

Happened when not shifting- once character moved away from edge, fire went out