Content type service unable to determine prefix

Using testsuite-1.06.01, I add the mixin "taggable" to the demosite:newsdocument (in the CMS Document Type Editor) and commit my changes. Now, the nodetype node under hippo:namespaces has a new "supertype", while the CND is not aware of it. Then, I retrieve the ContentType for this document

http://localhost:8080/site/restservices/contenttypes/ct/demosite:newsdocument

Note: the prefix is null, and the name is a comma-separated list of type and taggable mixin.

This behavior is currently a problem for the way Essentials deals with document type modifications.