I guess I need to look into it but adding preferences to a remote portlet shouldn't be possible since only the producer can do so i.e. the consumer doesn't have any control about the preferences/properties a portlet exposes via WSRP. The only thing that can be done is read/set values.
That said, Portal should handle the scenario better. Can you please open a JIRA for it, please?
a JIRA has been created:
I haven't read carefully the WSRP documentation, i should not create new properties on a remote portlet :-)