Burning skeletons dont shoot any flaming arrows at regional diff >3

Skeletons are supposed to shoot flaming arrows with a chance of 50% when they are burning. They don't.

 

Reproduce:
1. Set up superflat creative world

2. mobspawning false (no other monsters annoying)

3. time add 150d

4. summon skeleton without flame bow

 

-> The skeleton should shoot flame arrows now, but doesnt. Also doesnt work when igniting it with flint and steel, fire aspect etc.