I don't know what was causing the form to display improperly in IE, but I resolved the issue by going back and creating a new form and inserting it on the page. The first time I tried this it failed. I was editing the layout quite a bit, rearranging field order and the such, but the third time, it seems to have worked.
One symptom was the appearance of a blank field at the very top of the form, perhaps similar to what was reported in this post: <a href="http://wp-types.com/forums/topic/empty-input-field-appearing-at-top-of-cred-forms/ " >Empty input field appearing at top of cred forms</a>
In any case I have resolved this for one of my forms and have two more to work on.
