I have eDir groups that are Also GW Distribution List

If I create a user & add him/her to a GDL then this membership shows
instantly also on the membership tab in C1

But if I create a user & add him/her as member of the eDir group (and do not
explicitly add GDL to this user), then this user is NEVER member of this
GDL (does not receive emails) & his/her GDL tab is empty

I tried all sorts of Sync options & none makes any difference

Anybody any idea?