I recently upgraded IER from 18.104.22.168 to 22.214.171.124.
After sending a reply and returning to Pegasus in preview mode, the window with message text drops to a 1/4 of it's full size, complete with scroll bars horizontally and vertically.
It seems to only happen if the message that you are returning to after a reply, has html in it. All is ok if the message you are returning to is plain text.
When I select a different message or folder the message text window draws properly again.
When I downgrade IER to 126.96.36.199, the problem doesn't appear. So certainly seems to be an 188.8.131.52 issue.