Thunderbird uses last alias (in alphabetic order) as organizer an CalDav calendar item

I use Thunderbird as my email and calendar client for my mailbox.org account with a my custom domain. This works fine, except for one issue.

When making an new calendar item, I would expect the organizer of the meeting to be my default email adres (say default@mydomain.org). This is not the case, it is the last alias defined (first is was webmaster@mydomain.org, after I added the new alias zz.thunderbirdtest@mydomain.org, thunderbird uses that as the organiser)

I configured Thunderbird as descibed in https://kb.mailbox.org/en/private/addressbook-and-calendar/caldav-in-thunderbird/ using as username the my default mail address: default@mydomain.org.

Since Thunderbird does not know my mailbox.org aliaslist, nor my zz.thunderbirdtest@mydomain.org address. I assume mailbox.org is communicating this in some way to thunderbird as the owner of the calendar.

Is this correct? If so, can that be changed to the default adres