Maps can only lock once instead of several times

I made an 128x128 platform to "draw" maps and lock them in Cartography table so I can draw again and again the same area and don't make several platofrms... I think Maps were suposed to lock a lot of different times to show the proggress of each area. If I'm wrong please ignore this report. If I'm right please make the maps to lock several times and sowh different pictures, because now the same area can be projected twice, one in the locked map and one in carrent state.