EP6 - user group within user group ...how does it work?

Hi gang

how exciting to have a security forum at last - a good addition to SDN.

Anyone any idea why the following happens to me in our Portal (EP6 - sp15, PM & HCM):

I assign some roles to user group A. I assign some different roles to user group B. I assign user groups A and B to a third user group, C. I assign some users to all groups. Users in group C have no access at all, neither when they log in, nor when we look at their roles assigned. Direct assignments to groups A & B are fine.

What is the point of being able to assign a group to a group if this is the result, or am I looking at a bug?

Expectantly yours,

Andy Min