Disabling an email invite in the web GUI does not work

on my nextcloud installation, I’ve setup email notifications for calendar, that means
Groupware → Calendar Server → Send invitations is activated.

Whenever I create a calendar entry and add an attendee, that person gets notified for that event. Once in a while, there might be attendees that I do not want to receive any emails. My understanding is that the option “Send e-mail” for a specific attendee would control that. However, regardless if that setting is enabled or not, the attendee will always receive an email. Do I get something wrong? Is there a config setting which overrules the GUI option?