All the exploration information is lost when the map is zoomed out.
1- Create a map with 8 papers ad a compass in the middle.
2- Go to a previously unexplored region.
2- Activate the map.
3- The map information will be filled, and visible, covering almost the entire map (which is at 1:1 zoom level).
4- Go back to the crafting table, zoom out the map using the recipe with the filled in map in the center, and 8 pieces of paper around it.
5- Take the zoomed out map from the crafting output (same map with 1:2 zoom level).
6- Look at the map.
*The zoomed out map is 1/4 full
*A few pixels are filled in on the corner, where the corner is relative to where the crafting table is compared to the map center (see screenshot, in this example the crafting table is about 2 minutes of walk from the edge of the map).
Screenshot attached. The image in the screenshot should be impossible to get, since the map should be zoomed away from the center, and empty maps cannot be zoomed out. I have created a total of 3 maps, the same problem happened in all 3 in all 3, at all zoom levels (expanded all of them to 1:8).