Likely reproduction steps:

• Revision R has multiple package reviewers, owned by users A and B, both of whom are non-authors.
• Open a window as user A and prepare to accept.
• Open a window as user B and prepare to accept.
• Submit window A.
• Submit window B.

Expected: goes through cleanly.

Actual: Dialog with error: Reviewer "PHID-OPKG-xxx" is not a valid reviewer which you have authority to accept on behalf of.