Just verified your statement. The explored map always does disappear. I expected about 1/4 of the zoomed out map that was previously explored to remain explored after zooming out.
(This wasn't too noticeable to me due to the player's large radius for uncovering an unexplored map, But when zooming to the final zoom step it becomes evident.)
Note regarding the severity: I spent many hours fully exploring a map and it was the opposite of fun to find out all that exploration was a waste and the info lost after zooming out the map. I'm sure I'm not the only player to encounter this.
Steven Bowdridge
@Marcono1234
Just verified your statement. The explored map always does disappear. I expected about 1/4 of the zoomed out map that was previously explored to remain explored after zooming out.
(This wasn't too noticeable to me due to the player's large radius for uncovering an unexplored map, But when zooming to the final zoom step it becomes evident.)