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.

Thanks

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.