9.0.4: How is "Mail Sender" determined in Object Activity Log?

I have a ticket which I edited some days ago.

In the Ticket's history, I correctly can see that I edited some of its attributes.

According to the Ticket's activity log, however, the notification mails where sent on behalf of a colleague who has nothing to do with this ticket. I find this confusing, why has she been chosen by ProjeQtOr (She's not creator nor assignee of the Ticket and hasn't touched it as far as I know. I think she even does not have permissions for the Ticket's Project.)?

(I could not check what was contained in the actually sent mails, as I disabled "send mails to myself" in the setting.)

Maybe relevant: I activated the "combine sent mails" setting (not sure how it's actually called in English) to avoid too much individual mails to be generated.

Excerpt of the (correct) history view, which shows my modifications:


And here are the corresponding notification mail entries of the Ticket's activity stream:


I tried to anonymize the snipped, but you can clearly see it's not me who's shown there.

The user who "sent" the mails according to the activity stream does not have admin permissions.

Those are her project allocations:

"Profile" is "Project Member":