Assertion `type.type_kind() == XQType::ATOMIC_TYPE_KIND' failed

The following query and schema cause an assertion to fail.

src/types/typeops.cpp:145: static zorba::store::SchemaTypeCode zorba::TypeOps::get_atomic_type_code(const zorba::XQType&): Assertion `type.type_kind() == XQType::ATOMIC_TYPE_KIND' failed.

-------------- query --------------

import schema namespace f = "http://www.evaluescience.com/schemas/forms" at "forms.xsd";

declare namespace an = "http://www.zorba-xquery.com/annotations";

declare %an:no-cache %an:sequential function local:test2() {

   variable $form := validate strict {
     <f:form>
       <f:hidden name="myid" value="3"/>
     </f:form>
   };
   replace value of node $form/f:hidden/@value with "hello";

   "ok"
};

local:test2()

-------------- schema --------------

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

    <xs:complexType name="Form">
     <xs:sequence>
      <xs:any namespace="##targetNamespace" minOccurs="0"
       maxOccurs="unbounded">
      </xs:any>
     </xs:sequence>
    </xs:complexType>

      <xs:element name="form" type="Form"></xs:element>

    <xs:complexType name="Hidden">
         <xs:attribute name="name" type="xs:string" use="required"></xs:attribute>
      <xs:attribute name="value" type="xs:anySimpleType"
            use="optional" />
    </xs:complexType>

    <xs:element name="hidden" type="Hidden"></xs:element>

</xs:schema>