Can you post the link to the Microsoft thread on this topic?  This just started happening with a number of our users.

Our current workaround is to:

1. Create the new email via QB

2. Delete the body provided by QB if required (in our case, we have our own Outlook signature or template that will be used)

3. Toggle the email format from HTML to Plain Text, then back to HTML (this is the workaround that solves the problem for us)

4. Make changes to the body of the email and send it as normal