Hi
i have had this as an ongoing issues for ages and all MS can say is turn of add - in and create a new profile. non of these make a difference at all and still experience the problem.
from my testing it seems to be related to the rendering of the HTML message. the work around i have found is restart outlook ( not really good enough) or to change message format from HTML to PLAIN or RTF and then back to HTML. again not really a good enough
solution.
even had it when a person was typing and e mail and was half way through. another e mail arrived which he went to reply to but experienced the problem where he could not click into the e mail. went back to the half written e mail which was not totally blank
and could not click into the body.