Formatting is lost in forwarded emails

When I forward an email that was received in HTML, all of the original text changes to a fixed-width font with no word wrap. That is each paragraph is now a single line. This is seen in the composition window before and after choosing a message recipient. It is also seen in the preview window in the sent messages folder after the message is sent. The new text that I type in at the top can be formatted. It is only the old message content that gets changed. If I do a shift-forward, everything still gets converted to fixed width, but word wrap is back. There is no formatting toolbar. I have the convert to plain text box unchecked. This problem started after the update to version 45. I have disabled all of the addons.