A little more information: when I tried again on the school site, I found I couldn't establish a pattern--on initial entry both looked good. Then after some selecting of Update Assignment and using the jump forward & back arrow I got 100% width again and couldn't get it to go back right. In the end I defined a div.bodytext class with the desired width percentage in styles.php, and that seems to give me stable results.
Incidentaly, is there a way to move Due date and Maximum grade so they display at the end of the user text instead of at the start? That way they would appear just above the submission status and form.
Thanks,
Jim.