[quote user="Jon Summers"]Aha! Does that happen somewhere inside mdlTag_create?[/quote]
Yes.
[quote user="Jon Summers"]Presumably, if the host already has an origin assoc. point,[/quote]
This statement doesn't make any sense...
The "origin" of a shape is always vertex 0. The assoc point dependency linkage added to the tag element basically says, find the shape I refer to and return the location of vertex 0...the shape isn't modified, there's no "origin assoc" added to the shape, the shape just has it's geometry.