I have Microsoft Office 2003 on a PC. Just switched from Norton Anti-virus to McAffe.
When composing a reply to a message, the message disappears. I can locate the partial reply in the McAfee Anti-Spam folder.
I noticed that the McAfee Anti-Spam folder was a 'child'/sub-folder of the Inbox, so I moved up one level as a to the 'sibling' level and will watch to see if this helps.
Doubt that this is a solution, so any idea why this would happen?