Google has posted an announcement thread at Google Groups saying they hope they have fixed a bug that removed ownership status of some Google Group owners.

In short, Google Groups pushed out a new update that caused the removal of ownership in some instances. Google believes they have addressed the issue and returned ownership status to those impacted by this change. Google said:

Those impacted by this issue had to have meet the following conditions:

you have multiple email addresses associated with your accountyou attempted to log in while the bug was liveyou subscribe to or own groups under the different emails in (a)

Forum discussion at Google Groups.