I have the same problem.
I can use my map in MTA, I can edit it and everything but I can't find where is it saved.
I tryed in C:\Program Files\MTA San Andreas\mods\map_editor\maps but it's not there... I have some old maps from old version.
EDIT: I found the solution so here it is for anyone with the same problem. Look for C:\Program Files\MTA San Andreas\server\mods\deathmatch\resources