You should do some debugging there. The map, you are passing, does it contain all the keys? Try to print them out. When game loads, does the map contain all the keys? It should really work out of the box. I have maps in my savegame, and they work fine. Probably you are passing a map that has only last key. Or you are reading it wrong. Try to debug these two.
Every map has keys node. Iterate through it to make sure you have them all when passing it to the save game, and when you are reading the savegame information.
