I started a game (600AD, current SVN) as Japan and went for the usual route (Monotheism -> Alphabet -> steal all of Chinas/Mongolias techs), stealing 6+ techs. never did my spies get any XP for it.
I always let them wait for the -50% bonus, maybe thats the cause?
However i think I once stole some gold from their treasury and maybe got 1 XP point for it...definitely not enough for a promotion but i think the great spy counter moved.
sorry, will be away from my PC until Sunday, so cant provide saves until then