I have set un an account with a child account.
When I want to create an appointment in one of the child account calendar, I have an error if I set an attendees.

The error is :
Unknown error (mail.MUST_BE_ORGANIZER).
method: [unknown]
msg: You are not Organizer in call to: CreateCalendarItem

If I don't set an attendees the appointment is created. I can edit the appointment after to add the attendees but they don't receive the invitation mail.
Also after I get the error all the buttons on the appointment tab are greyed out the only thing I can do is close the tab and recreate the appointment from scratch.

Any ideas to fix this or am I doing something wrong?