Issue with Outlook Meeting

For a meeting, if few of the mandatory participants send acceptance and later on when the meeting requester updates the meeting, the attendees who accepted the meeting are being marked in optional attendees. This gives a wrong information that those attendees are not mandatory for the meeting, although they were in the mandatory list in original meeting.

1. How do you access your account? Is it through browser or Office Outlook? - Office outlook
2. If you are using Office Outlook then which version of Outlook are you using? Outlook 2013
3. What type of email account have you configured? Is it POP3, IMAP, Exchange Active Sync or Microsoft Exchange Server email account? Microsoft exchange server email account
4. Have you been sending the initial/original meeting invite to attendee’s alias rather than actual email address? initial invite is sent to alias and not individual email address.
   

Regards,

Priya