[GAMEPLAY] Gangplank kegs not applying Lich Bane damage properly

With a Lich Bane in your inventory as Gangplank, directly use Q on a minion (ensuring spellblade was used) -- note the approximate damage. Next, place a keg, wait for it to tick down, then use Q on the keg (once again ensuring spellblade is used). If done correctly, the Q'd powder keg should do LESS damage than the direct Q. This may not be noticeable vs champions -- as the increased keg damage vs champions may offset lost Lich Bane damage. Does this have to do with kegs forcing physical damage, while Lich Bane forces magic?

I know this isn't very urgent considering AP Gangplank is not popular, but it was very irritating to experience, and kind of kills the desire to play him in off-meta ways.