Demo'd at https://test-optho3llvh27.phacility.com/D1. Replication is:

Make a project with a milestone; add a user to the project. Make an Owners package whose package is that milestone, which adds itself as the reviewer on diffs. Create a diff that triggers the ownership rule.

If the user accepts the diff, the group reviewer will not show as "accepted," despite them being a member of the group, and said member having accepted the diff.

Phabricator 216f6be11ece53cb1daafc8fff636dbdb0d7ef3d, but replicated on demo Phacility instance, as noted above.