For the Season 9 PUP, the new version of Incendiary Arrows gives all arrow/bolt units a Siege arrow/bolt. This is supposed to be used against buildings. However, it is being used against Siege units as well.
This completely ignores the new Ranged Armor Resistance of Siege Units.
For example, after researching Incendiary Arrows, Archers/Crossbows/Horse Archers all use their 3/4 damage Siege arrow/bolt against Mangonels, Trebuchets, and all other Siege units.
PUP Build: 12.0.1663.0