Outlook 2013 Calendar Entry Dropping Invitees

I am seeing an reproducible problem where (seemingly) random invitees are dropped from an Outlook calendar entry.

I have been able to replicate this as follows:

1. In Outlook, create a new Meeting Request and add two email addresses. Set subject & location and save it.
2. From one of the invited email addresses, accept the calendar entry
3. In Outlook, edit the Meeting Request and add another email address. Send the response to all invitees.
4. From one of the invited email addresses, accept the calendar entry
5. In Outlook, open the Meeting Request. You will be missing one of the original invitees.

My main email account is attached to Outlook in Hotmail with a custom domain.

I'm running Office Pro 2013 x86 on Windows 7 x64. All the latest updates have been applied. I was able to replicate the problem when the invitee email/calendars are hosted by Gmail and by Yahoo.

Has anybody seen a similar problem with any environment? It's causing more than a few meeting problems.