Compatibility with IE 7

The id attribute is required in a form tag in XHTML, the name attribute is required in the form tag in HTML. You have neither in the form in the last div displayed.

The id attribute is required in a form tag in XHTML, the name attribute is required in the form tag in HTML. You have neither in the form in the last div displayed.

XHMTML id is NEVER required. name isn't required for form elements ( or even fields ) in HTML. It's optional. Not every form needs a name or id; not every form is necessarily accessed via javascript/CSS etc. Even if every form was accessed by javascript/CSS, it wouldn't need a name or id. id is always optional; it's defined in the XHTML core module for all elements as optional; as far as I know, so is name in HTML.

http://www.w3.org/TR/xhtml-modularization/dtd_module_defs.html#a_module_XHTML_Common_Attribute_Definitions
http://www.w3.org/TR/xhtml-modularization/dtd_module_defs.html#sec_F.3.4.

If you can't read DTD, these are the relevant fragments from the XHTML DTD with commentary:

<!ENTITY % id.attrib
     "id           ID                       #IMPLIED"
>
( id.attrib is a DTD parameter entity in the syntax for an optional [ implied ] attribute, of type ID with name 'id' )
...
<!ENTITY % Core.attrib
     "%XHTML.xmlns.attrib;
      %id.attrib;
      %class.attrib;
      %title.attrib;
      xml:space    ( preserve )             #FIXED 'preserve'
      %Core.extra.attrib;"
>
( The id attribute is 'copied' into a list of core attributes; later, core attributes is copied into a list of 'common' attributes, but, take my word for it, I'm not gonna copy that one )
...

<!ATTLIST %form.qname;
      %Common.attrib;
      action       %URI.datatype;           #REQUIRED
      method       ( get | post )           'get'
      enctype      %ContentType.datatype;   'application/x-www-form-urlencoded'
>

( The 'common attributes' [ which contains 'core attributes' ] are copied into the attribute list for form, where other, form-specific attributes are added, notice, only one if them is 'required', the rest have non-fixed default values ).

Thus - id is optional in forms.

Sorry that's a little off topic and absolutely useless to the OP... but.. so was your comment; and it really needed correcting.

Then this guidebook I have is wrong. It says that name is required in HTML, id is required in HTML.

Sorry about that. It was the only thing I could find that looked out of place.

The only other thing I can think of is that I have occasionally had IE render two things in the same place, hiding one if them.

It would help to see the stylesheet.