minecraft item (level1) map are not adjacent

so playing minecraft for a few years and is seen this a lot of times when i use a level 0 8x8 the sides matches next to each other but when i put a level 1 map 2 of them next each other it creates a a single space between the maps so it doesn't appear on the map

is this a actual bug or is there a reason why the line with green emeralds don't show up?