Minecraft 13w38c, Minecraft 13w41a, Minecraft 13w41b, Minecraft 13w42a, Minecraft 13w42b
If you disconnect from a SMP server but keep minecraft open, then reconnect to the same server, maps you viewed in your first session stop updating player locations. Your old location still is there, but it doesn't update as you move around. If you quit the game completely, and restart it using the launcher, and rejoin the server, the same maps work again.
Similarly, if you reload a world in single player, you have the same problem.
Note that this is not a dup of
MC-3416 or MC-31731. (I get those bugs too, if I use framed maps, but this is different. MC-3416 requires a server restart to fix, this issue is fixed by client restart.)