Can't get automatic weights working with a hand

Hi, I created a hand and its armature, now I’m parenting both together with automatic weights, but it’s useless as weights between fingers are mixed.
First I had only one bone for the hand so I added a bone for each finger but that doesn’t change anything.
What can I check ? How does it work to find the correct group for each bones ?

A video of my problem.


Hi, You will have to manually paint the weights for each of the bones.

OK, but if this is the only solution, it’s seems to be a bug.