Mist pass breaks with transparent textures in Cycles

I’ve never been able to figure out how to fix this. Transparent textures create this white noise that makes the mist pass unusable. Does anyone know how to fix this?

It’s very apparent in the trees behind the characters, and also the hair on the horses neck in the foreground. That should be as black as everything else.

Would be very grateful for any help, this has been driving me crazy for a loooong time. Perhaps a mist pass is not the best way to get a depth pass?

Cheers

It is a known issue. See:
https://developer.blender.org/T66149

I’ll try to find the thread were some workarounds are posted.

I was thinking of this post and the one after it.