...unfortunatelly - it's not related to Location settings as we are testing this behaviour from the same Location settings:

We are simple switching via File-Security - Switch ID between A1 and A2 and effective access results are different!

P.S: Environment is IBM Notes/Administrator R9.0.1 standard client on Win64

I'm struggling to know exactly what you're observing. Could you tell me, what are A1, A2? Are they person names?

Next, by "same group membership", you mean they're members in identical groups in the NAB?

Are either listed individually elsewhere, such as in "administrator access" on the Server doc?

In any event, here is the oddity I ran into with the Effective Access dialog: when the group is listed as a "person group" *and* the capitalization isn't the same on an ACL as it is in the group, the Effective Access dialog can miss the group. I'm not entirely sure what the exact situation is, but I found it was pretty easy to reproduce. The group name I ran into, it was all alphabetics & spaces. The group itself was listed as "multi-purpose" on the NAB.

Mike, thank you for sharing your experience - however, our problem was not related to person vs group duplicity....

After deep investigation, we have found out that:

When the administrator A2 was lisetd in Full Acces Administration of Server document, the effective Access dialogue for him (A2), didn't show his group membership.

For every other analyzed user (even the other Full Access Administrator) the Effective Access dialogue showed group membership!.

Note: The Full Access mode was node enabled during this observation....

Really strange, but reproducible (at least at our Domino system) :-)

Release 9.0.1

Revision 20131022.1138 (Release 9.0.1)
Standard Configuration
L-GHUS-968PRV