The section on fn:deep-equal (14.2.3) describing comparing element nodes is written based on the type annotation.

Nothing is written in case type annotations are stripped, or when validation is not requested. This process would lead to element nodes receiving the type annotation xs:untyped. This type itself is not clearly defined as "complex content"  type in XDM 3.1 since it doesn't have a defintion (though this can be inferred from its intended role).

I don't think there's an error per se, but I propose we clarify this most common case, for instance with a Note, proposal:

<proposal>
Note: when nodes have not been validated, have been stripped from their type annotations or have been created from an InfoSet, the type annotation of element nodes is xs:untyped [reference to relevant section in XP31?]. For the purpose of this section, xs:untyped should be treated as a complex type with mixed content.
</proposal>