Does anyone know why units converted by missionaries don't count towards the Steam achievement "Wololo"?

As the title says, I’m most of the way through the “Unexpected” achievement, to convert 100 units with Spanish Missionaries. However, these conversions don’t count for the “Wololo” achievement, to convert 1000 units. I can understand that it might be a monk vs missionary thing, but if it is, it should really say “Convert 1000 units with monks”, rather than “Convert 1000 units”. I’m not sure if it is counting my conversions with monks either though, so it’s possible that it is related to the fact that I’m playing a campaign (El Cid 2), in quest of achievements. Anyone know why this is?