Using multiple cartographer villagers (I used 4), I received the same map (same background too) pointing to the same trial chamber, even though the maps have differing IDs. The bug is not occurring on the Woodland Mansion maps. 

Note: This is occurring on a server. I tested it again in a creative world and it worked fine, excepting the bug where the icon doesn't show up on one of them (another bug for another report)

Update: It seems like leaving the other cartographer alive might be necessary to get a new map, but I don't think this is intentional as the other structures give a different map even if the previous cartographer is dead. Before, I was killing the cartographers to make space for a new one, but this time I made two, and the second one gave a new map. Like I said before, this is different to how the other maps have been acting, as when I replaced the cartographer previously, I got different Woodland Mansion maps.