Portal administrators are unable to share private items owned by another user to a group that is also owned by the user.

Workaround

Share the item from the user account instead of the admin account.

Alternatively, perform the following workflow:

1. From the admin account, go to the item and click Share.
2. Set the sharing level to Organization and save the setting.
3. Click Share again.
4. Share the item with the group and save.
5. The item is successfully shared with the group (in addition to being shared with the organization).
6. Click Share again and change the sharing level from Organization back to Owner, and save the changes.
7. The item is now shared with the owner again and with the group.

Steps to Reproduce