I have looked in the current LASORS and in Section E para E1.5 Important Note Para 3 It says
'SPA IR privileges are not type or class specific -the holder of more that one SPA type or class rating is required to re-validate the IR on only one SPA type or class (usually the most complex one). However, the holder of a ME IR must revalidate on a ME class or type.'
I think the confusion in the later posts in the thread comes from talking about the SEP rating itself and using renewal and revalidation interchangeably.
To revalidate an SEP class rating by experience one needs 12 hours in the last 12 months including a dual flight with an instructor. The dual flight requirement can be satisfied with any other flight for the grant, revalidation or renewal of a rating. In this case the MEIR holder can revalidate the IR, combine it with the MEP rating proficiency test and use the flight to get the one hour dual for SEP providing that they have or will have sufficient SEP experience when that rating expires.
If however one needs to revalidate the SEP rating by test then the discussion of the IR etc is not relevant and the proficiency test must be done in an SEP aircraft. The same goes if the SEP rating needs renewal, which must be by test in an SEP aircraft.