I cleaned up my usergroups to a bare minimum. Registered has a styling priority of 100. I have a couple others in between, but Moderating is set to a priority of 1000.
The banner I have for Moderating displays correctly, but on one moderator, assigned the exact same usergroup as our other moderators (and also displayed as "staff"), still has a username in the default color, not the green/oblique style as the others. Primary usergroup is Registered, secondary is Moderating. No others are selected. They are also both assigned as "Moderators" (aside from selecting the usergroup).
Inspecting the username, the CSS element .username .style4 (if I'm not mistaken) is being applied to the other moderators but not this one.
Switched back to the bone stock default theme, no change. And I run minimal add-ons. Although I don't see why one member with the same usergroups should be any different from another.
Where to look next?