I created a map and used it. Everything went fine.
I created a second map and used it as soon as i reached the edge of the first map. The second map worked fine.
Then i went back from where i came and used the first map again but the contents dissapeared. I got a blanco map with a few dots on it.
The second map was still working. I placed it back in my inventory and back in my hand but first stayed blanco.

Solution: I closed the game and restarted it and both maps worked again.

Just like some other bugs (example painting that shows up only after restarting) it is not really critical but more annoying as we need to restart the game.