We flew back to LHR on 30th December CE with a similar situation. Announcement made that no loose nuts would be served throughout the aircraft due to a passenger in ET with a severe allergy, however the CE dessert was some sort of date cake with a nut topping and this was served to CE passengers. We queried this with the cabin crew member who agreed it seemed anomalous but they thought that, as the nuts on top of the dessert were not loose but "cemented" in place with a sugary glaze this probably would not pose a problem.