custom archetype-catalog.xml not read

I try to create a custom archetype-catalog.xml and use it
"mvn archetype:create -DarchetypeCatalog=file://tmp/archetype-catalog.xml"

but the displayed list is empty, (you could try with the https://svn.apache.org/repos/asf/maven/archetype/tags/maven-archetype-2.0-alpha-1/archetype-common/src/main/resources/archetype-catalog.xml)

And if I copy on a http server :
"mvn archetype:create -DarchetypeCatalog=http://scala-tools.org/"
Then I got an exception
java.lang.ClassCastException: org.apache.maven.archetype.catalog.ArchetypeCatalog
at org.apache.maven.archetype.ui.DefaultArchetypeSelectionQueryer.selectArchetype(DefaultArchetypeSelectionQueryer.java:97)
at org.apache.maven.archetype.ui.DefaultArchetypeSelector.selectArchetype(DefaultArchetypeSelector.java:179)
at org.apache.maven.archetype.mojos.CreateProjectFromArchetypeMojo.execute(CreateProjectFromArchetypeMojo.java:165)

It very critical, because our user can't create new project from our archetypes.

(workaround : "mvn org.apache.maven.plugins:maven-archetype-plugin:1.0-alpha-7:create ..."