[quote user="Brien Bastings"]mdlAssoc_createOrigin will be called with the ElementId of the base element[/quote]
Aha! Does that happen somewhere inside mdlTag_create? Presumably, if the host already has an origin assoc. point, that call is by-passed.
Suppose I create my own origin assoc. point on the host before calling mdlTag_create: does the tag then get associated with my origin point?