This was an event item, so I assume you got it from a box and not from the pearl shop. Sadly, these items you get from RNG boxes are not tax exempt like directly bought pearl items, and the Value Pack does not work on them either. It's not a bug, just an unfriendly mechanic.
When I sold [Event] Classic Outfit Box, it didn't apply the value pack tax reduction. The pre order price is 1,310,000,000. So with the Value Pack, it should have given me back 1,106,950,000. And you can see I do have a Value Pack at the time when I sold it.
I can clearly read "+30% Silver Collection upon Central Market Sales (Excluding Pearl Items)" in your screenshot and you still say Value Pack Tax reudction not applying on Pearl Items is a bug?