Xmllint using XSD+XMLCatalog cannot find uri - validation

Question

I am trying to use xmllint with an XSD file that uses one xs:import without the #schemaLocation attrib set. (In OxygenXMLEditor this setup is working fine)
XSD relevant section:
...
<!-- this one is the trouble -->
<xs:import namespace="http://www.w3.org/1999/xhtml" />
<!-- this one is resolved fine -->
<xs:import namespace="http://www.idpf.org/2007/ops" schemaLocation="conf/b.xsd"/>
...
Given this XML Catalog file:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD XML Catalogs V1.1//EN" "http://www.oasis-open.org/committees/entity/release/1.1/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
<uri name="http://www.w3.org/1999/xhtml" uri="file:///home/me/code/base5html.xsd"/>
</catalog>
Ok, then I run it:
$ export XML_CATALOG_FILES=~/code/mycatalog.xml
$ export XML_DEBUG_CATALOG=1
$ xmllint --load-trace --noout --schema myschema.xsd test_doc.xml
Result (approx):
Loaded URL="myschema.xsd" ID="(null)"
Loaded URL="conf/b.xsd" ID="(null)"
Loaded URL="c.xsd" ID="(null)"
c.xsd:17: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.w3.org/1999/xhtml}p' does not resolve to a(n) element declaration.
c.xsd:18: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'ref': The QName value '{http://www.w3.org/1999/xhtml}cite' does not resolve to a(n) element declaration.
c.xsd:26: element attributeGroup: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}attributeGroup', attribute 'ref': The QName value '{http://www.w3.org/1999/xhtml}normAttrGrp' does not resolve to a(n) attribute group definition.
...
(more taken out)
...
WXS schema public/ctrl/lov.xsd failed to compile
Loaded URL="myschema.xml" ID="(null)"
Q: Isn't XSD+XMLCat a supported feature in libxml2 ?
( No hints to be found anywhere on the homepage : http://xmlsoft.org/catalog.html )