Looking at the description where it says "through the shadows" and "need to be able to see the target" while it's debatable I'm pretty sure the intended behavior isn't through the wall.Not going into a vault is a bug fix. Not being able to shadowstep to other side of a normal wall is nerf.
Sure it's a nerf, but don't think it like it was fine and now nerfed. Instead think of it like bugged and now fixed.
On a side note if Shadowstep is fixed like this I think the Cursed skill that goes through the walls should act the same.
Just to put things into perspective, I think there are four skills going through the walls: the two mentioned above both of which are quite spammable and include an attack on top. The other two are Dwarven racial and Probability travel, both of which don't have attack included and their cost is way higher than the other two.
Edit: Dwarf thing isn't costly, but it has 45 default cooldown and Probability travel has limit to how often it's used on top of hefty 200 mana sustain. Both of these are highest tier talents while Blindside is lower tier.
If Shadowstep gets this "nerf" I'd say blindside definitely needs the same.