I've noticed for awhile now that the maps all seem to have some kind of linked zoom with the camera zoom. Happens both with the regular mission map that you pull up with the M key, and the mini map in the corner.
It seems that when you set the zoom for one, it translates into the others, both space and ground.
Example: I could get a ground mission in an exploration cluster, zoom it in, and then when I finish the mission and head back to sector space, my ship is zoomed in.
Then when I zoom out for the ship, and look at a map again, the map in zoomed out.