All attendees receive notification when adding new invitee

In the past few weeks I've had the issue that when I add a person to an existing event in the Outlook calendar, all the participants receive a notification/email!

The prompt to update only to new participants or all doesn't appear like it used to.

It is really annoying as it creates confusion and spamming (we have many large meetings with many quite VIP attendees). Why has this been done, and what can I do to ONLY send to the new person that I want to add instead of all the attendees? 

Thanks