Members in the DL were put on Cc: list after updated outlookMeeting Request

My company user sent a meeting request to several DLs in Outlook. After a while, she opened the meeting request and just renamed the meeting subject name (without any change on the attendees list). After she sent out the updated meeting request, some of the members name in the DLs were listed on the Cc: list. But that several DLs are still on the To: list. Just wonder if this is normal in Outlook.