(Upvote please so Riot can see it fast)
Riot did an intentional change to Ezreal's Q this patch so it can apply spell effects (like arcane comet) but it's not in patch notes. However, Muramana deals damage on single target spells, and also as on-hit damage.
Ezreal's Q now deals double damage from muramana and that's why his winrate increased by 10%. I think it works the same with Gangplank's Q