In 1.6.4 the maximum map size will not craft properly. When attempting to craft the 2048x2048 size map a map is craft but its the same size as before (and exact same map as before). In 13w39b the problem problem is more serious, and appears when trying to craft the 3rd map / second up-grade / 512x512 map, simply returning the 256x256 map that was put in. This seems to apply in both survival and creative mode, but I first discovered in in survival (used creative for further testing).

Steps to Reproduce:
1. craft a map
2. use the map once so its drawn
3. enlarge the map and return to step 2
4. keep repeating 2-3 until you should have the 2048 (or 256) size map,
and you will start getting out the same map you put in.