Can't expand the group members after click + from To field

Reproduce steps:
1. Create internet group in Domino directory with mail domain & group internet address.
2. Open outlook, create a new memo, select the created group from domino directory.
3. The group name is added in To field, the group name is prefixed with a plus sign.
4. Click the plus to expand the group, hit errors. The group can't be expanded to check the group members, but the mail can be sent successfully to the group members.

This is known limitation, but customer like to make this work. Since the end user can't check the group members from outlook, sometimes they don't know if the selected group is expected one. Thanks！