Duplifaces do not get instanced when using parent as object for particles

Hi,

I looked into BBB’s sets and I saw the nifty trick for the flowers in the field, they were instanced by a particle system across the grassy field. Together with weight maps one can control the flowers.

Nice, I thought, let’s do it with trees.

That works, but it turns out the leaves that are part of the tree are set up as duplifaces.
These are not instanced.

Bug ?
Or feature ?

grtz
wzzl