Militions turn into marines

Hello,
i was playing a game, when suddenly the next turn started all my militia troops that weren't placed in a defensive line turned into marines, is this even possible?

I am sure that isn't possible, elaborate more please.

So I'm putting up a defensive line, I needed to move my militia over a bigger distance, so it took me a few turns, when I only had to move a few more. the unit's I had to move where gone the next turn, and instead I had marines. When before I had only my marines in the area I was fighting in (china to be precise) and the milita's I was trying to set up in Europe (Germany) where "replaced" by marines.

I'm certain there where no marines in this area, and certainly not one's that where spread out one by one over entire europe.

It's not that I'm complaining, since I can use them, but it's very strange nevertheless.