Lords changing religion?

[LawLeewer]

I have this list of lords of my kingdom, their fiefs and religion on Excel which is very helpful since I am the leader of my own faction.
So I decided that I would create a Pagan-only kingdom and I've been converting captured lords to Paganism ever since. It was working out well until the moment I noticed that one of the lords labeled as Pagan in my list was a christian now and I went to check if it was my mistake or if more of the lords coverted to christianism... for my sorrow most of the pagan lords on my list are actually christians now.

Does this happen with all the lords or just the ones that are converted when prisoners? If so, why is there an option to convert them if they are just going to go back to their old religion?

 

[Faenwulf]

There is always a chance for Lords to convert to the other religion. In my game, a Lord from West Seaxe has converted to paganism and paid me to raid a monastery in Ireland.