Steps to reproduce:
1. Hold an item in your hand from your hotbar that is set to be filtered
2. Open some sort of inventory and remove an item filter inside that inventory (middle mouse click)
3. Swap the item in your hand for the previously filtered item in the inventory
4. 'Quick-drop' the item (Q)
Notice that the quick-dropped item has ignored hotbar filter.
GIF to explain better than me:
