I think this is a serious issue, although I haven't been able to confirm if this is how it's supposed to work on cartridge.
I faced a RestTalk Mega-Gardevoir today and I believe that the Pixilate boost applied when it used Sleep Talk and picked Psyshock. Here's the replay:
http://replay.pokemonshowdown.com/oususpecttest-142964396
On turn 10 his Gard Psyshocks my Chansey and deals 32.5% damage. On turn 11 he uses Rest and I Softboiled. On turn 12, he uses Sleep Talk and picks Psyshock, which does 47.9% to Chansey, no crit or any change like losing the Eviolite to Knock Off - the only difference was that Gard used Sleep Talk.
As a reference, here's the calc for what I assume to be 252 Modest M-Gard against Chansey, although I didn't confirm the opponent's set:
252+ SpA Mega Gardevoir Psyshock vs. 252 HP / 252+ Def Eviolite Chansey: 228-268 (32.3 - 38%) -- 96.3% chance to 3HKO
And 47.9 / 1.3 (the boost from Pixilate) is 36.84, which is comfortably in that range.
It doesn't really make sense that the Pixilate boost would apply here - Psyshock is treated like a Psychic type move for purposes of calculating resistances/weaknesses (it would still be super effective against M-Venu even if I Sleep Talked it), so why should it get the boost for being Normal type? I suspect the code applies Pixilate when it sees Sleep Talk used, but I am pretty sure that is wrong, although like I said, I can't find any info on how it's supposed to work on cartridge.
Edit: shoutout to KlefkiHolder and Chagrilled for testing it, it appears it definitely is applying a Pixilate boost
http://replay.pokemonshowdown.com/customgame-142977328