The initial grab's always had a small check around the cursor for nearby units (nearest unit within a few hundred units) if something's not directly targeted. Is it possible that's what you were seeing?
|Regarding the W not grabbing I've seen that occur even when the sphere and cursor are both well within the spell's cast range so there's definitely some other cause.|
EDIT: Well, I couldn't get on the PBE, the queue seems never ending. I'll leave it going tomorrow in the background all day and wait for the "dunk" noise of it getting in.
EDITEDIT: Force of Will is working as intended (only grabs nearest sphere).