My form is using People Picker control and event receiver to add users to a People/Group field.
There's a problem with a user. First I added him to site collection admins, then using the form above to add his account to the People/Group field. After that, his name disappear from site collection admin list.
What could be the problem with the account? or something in event receiver may cause the mistake?
By the way, it's SharePoint Online.