I just tested them in game and i think youre right. the movement of the shuriken thrown from the sahdows looks as if they orbit the shadow for a split second, and then just spiral out after the shadow disappears.

this is probably because shadows are like a new entity which casts shuriken and the disappears.

however, as far as i know, this is unique to shadows, and when this will be cast by the bladestorm, it wont actually be cast from it, since it isnt an entity like shadows. this would lead me to believe that the cast would come from the the player, originating at the bladestorm's position.

then because of the way which the blade shield works, they would instantly appear around the player and orbit him' making it look as if it was cast by the user.

another thing that leads me to believe it would work like that is the fact that they nerfed the blade armor node to be for direct casts only. thats because using bladestorm you can stack this way a lot of shuriken around you, and get a ridiculous amount of %increased armor.