Second banner placed on map shows as completley black on map

I was playing with my friend on our server (powered by aternos) and was marking banners on a map, but the second banner would always turn black

Steps to reproduce: Grab a map (0/4) and banner

2. re-name the banner 

3.right-click the hitbox of the banner with the map

4. get a second banner

5. do the same thing (right click it with the same map) and see that the first banner is the right color, but the second one is black