Just had a game where the enemy Sivir dove under our turret to kill me, and survived, because her spellshield blocked our Jinx's chompers and Zap at the same time, while taking no damage from either. I thought this bug/coding was fixed.
Now I'm not a professional, but from my understanding this is an issue with the game's tic rate (<0.25 sec I believe, correct me if I'm wrong anyone). A tic rate is simply how often a game updates itself to what is happening. If two effects hit within the window of 1 tic there is no way for the game to be able to tell which spell hits first. so at that point you have two options: deny both or randomly choose between the two. Randomly choosing could easily screw over the Sivir/Nocturne/Banshee in question since it could just as easily make the spellshield useless in these cases.
tl;dr Not a bug, but technical limitations
Spell Shields blocking multiple abilities that hit at the same time, while not necessarily "intentional" in the strictest sense, is not considered a bug. The bug that existed was that Spell Shield was previously blocking EVERYTHING that hit in a single frame (or tick, if that's the case) including auto attacks, and the fix made it no longer block auto attacks.
