Edit:
Sorry, I still have this map#0 bug in my 1.4.2 world. But I created now a new 1.4.3 world and I can't reproduce the bug there. So it seems the map#0 in my 1.4.2 savegame is corrupted but for new worlds the bug is already fixed.
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This bug affects only the first map you create in minecraft (map#0). even when you craft a map of the same area as map#0
Reproducing the bug (in single player mode, not testet in SMP):
craft a map#0 and walk around
place the map in a item frame at a wall
craft another map#1
walk out of the area of map#0
use map#1
walk back to the wall an see that map#0 is blank now.
When you reload the world map#0 is visible again. The content of map#0 will disappear again, when you create and use the next map.
Linked issues
duplicates 1
Comments 3

no, MC-978 is a SMP issue. This is reproducible in single player mode.
Good news, SMP and SSP are the same codebase now.
Duplicate of [MC-978] ?