Happened twice that i have seen, Sion attacks red buff he dies but kills the mobs with his passive. When he respawns he spawns with the red buff. Not sure if this is working as intended seems a bit odd to me though.
In the preseason it was changed to where dying with buffs to monsters (either red/blue or the smite buffs) would keep the buffs when you respawned. I'm assuming it goes "Sion bled out with Red buff, so he died to monsters and keeps the buff" unless you specifically last hitted him (not sure on this at all).
working as intended I would geuss because your not supposed to lose it on executions anymore so if passive isnt autoed by a champ probably counts as execute
