I believe that K2-ComputeConAttr-54 might be wrong.

The only place that I can find a reference to the introduction of
a new namespace prefix is in XQuery 3.7.4 In-scope Namespaces of a Constructed Element.

The introduction of an implementation-dependent prefix will only occur when
the attribute is copied as a child of an element during element construction.

i.e. I expect the result of

<element>
{
  let $name := QName("http://example.com/", "attr"),
      $attr := attribute {$name} {()} return
    ( $attr, text { prefix-from-QName(node-name($attr)) } )
}
</element>

to be of the form

<element xmlns:generated-prefix="http://example.com/" 
         generated-prefix:attr=""/ >

and not

<element xmlns:generated-prefix="http://example.com/" 
         generated-prefix:attr="">generated-prefix</element>

Here's the XQTS query for reference.

(:*******************************************************:)
(: Test: K2-ComputeConAttr-54                            :)
(: Written by: Frans Englich                             :)
(: Date: 2007-11-22T11:31:21+01:00                       :)
(: Purpose: Ensure that a valid prefix has been constructed for a QName which th
e implementation is supposed to create a prefix for. :)
(:*******************************************************:)
string-length(xs:NCName(prefix-from-QName(node-name(attribute {QName("http://exa
mple.com/", "attr")} {()})))) > 0