We've just started to see some odd behavior recently. It is likely related to more clients rolling out at v9.0.1, where they had been 8.5.x and earlier.
Here's the issue: a user has a personal group set up in their address book to which then send a message. Used to be this group was parsed out to the individual members so that a "reply to all" worked just fine. Now, the message is sent as to the group name. However, a "reply to all" results in an error, as the recipient(s) don't have this group. I could set up a company-wide group, but then I have to maintain it. There is now an option in the 9.x client to "Do not expand personal groups" in the Delivery Options. By default this is not checked, so I would think the default action would be that the groups are expanded to the full list of individual addresses.
It would seem that there...