type not available during computation of function caching

The following query and schema cause an error to be raised because the schema type doesn't seem to be available when trying to determine if function caching should be done.

import schema namespace d = "http://foo.com/schemas/schema" at "schema.xsd";

declare function local:recursion($param as element(*, d:Content)?) as xs:boolean
{
  if ($param)
  then local:recursion(())
  else false()
};

local:recursion(<d:Content id="foo"/>)

<?xml version="1.0" encoding="utf-8"?>
<xs:schema targetNamespace="http://foo.com/schemas/schema"
  xmlns = "http://foo.com/schemas/schema"
           xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">

    <xs:complexType name="Content">
      <xs:attribute name="id" type="xs:string"></xs:attribute>
    </xs:complexType>

</xs:schema>

The error reported is:

type error [err:XPTY0004]: "[NodeXQType elementNode? content=[UserDefinedXQType Content@http://foo.com/schemas/schema isComplex emptyContent base:[XQType ANY_TYPE_KIND*] ]]": invalid type: not among in-scope schema types; raised at /home/mbrantner/zorba/sandbox/src/types/typeops.cpp:522