Currently, the player does not sneak walk off, but rather falls off the edge of the block.
Either way, I think that this should not be the expected behavior because achieving a step height increase then feels like a downgrade in some aspects (because you have to unlearn the muscle memory of sneak preventing you from falling off full blocks). If the player really wants to fall of the block, they can already do so by releasing their shift key.
This shouldn't be considered resolved.
Did you try actually playing with this? It feels really weird. The player can even take fall damage if the step height is large enough, potentially dying.