Outlook Emails with HTML attachments issue

We are on RT 4.2.12-5

When a ticket gets created from an outlook mail with HTML attachment it happens that the AdminCC email confirmation only shows the HTML attachment and not the mail, like the first “< div class=“WordSection1”> “ doesn’t display.
The ticket in RT shows correct. When I press reply or comment, I also only get the HTML attachment int the WYSIWYG editor, but when I switch off WYSIWYG I get the text of the attachment.

Now if the message is just an outlook mail, no problem, reply and AdminCC work fine.

FYI, I just checked with a Outlook mail received once with .txt attachment, and on reply / comment only the attachment shows…

It is strange and has been like this for years. Now I want to sort it out, any idea? Thanks.