Mobs killed by /damage with type set to wither don't drop wither roses

Using /damage with the damage type wither or wither_skull to kill a mob results in no wither rose dropping.

Reproduce:

1. Prepare a mob to get damaged 

/summon chicken ~ ~ ~ {NoAI:1b}

2. Run a damage command targeting the mob with the damage type set to wither or wither_skull 

/damage @e[type=chicken,limit=1,sort=nearest] 10 minecraft:wither

You'll see that the chicken dies but no wither rose drops.