The bug

The tag map_scale_direction is only read from a filled_map if it was created by scaling an existing filled map, but cannot be set when creating a filled_map item.

Note: This report is likely invalid because the tag map_scale_direction is only used internally and possibly also slightly hacky.

How to reproduce

1. Use the following command

   /give @p filled_map{map:32767}
   

2. Look at the map, its scale should be 3/4
3. Replace "###" with the data value of the map you just gave you (shown as "Id #X" in the hover text)

   /setblock ~ ~ ~ furnace{Items:[{Slot:2b,id:"filled_map",Count:1b,tag:{map_scale_direction:1,map:###}}]}
   

4. Take the map out of the furnace
5. Look at the map
   → map_scale_direction affected the map and its scale became 4/4
6. Use the following command

   /give @p filled_map{map:32767,map_scale_direction:1}
   

   → The scale is the default 3/4 instead of 4/4