EDIT: I didn't check on my maps for a day or two, but the next time I tried it seems my issue had somehow resolved itself and now the player marker is appearing and maps can be explored once again... I'm not sure what caused the hiccup, but I'm glad my maps were not permanently broken!

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Newly created survival world in 1.9 (single player). Spent some time mapping my surroundings and everything was going great, until today... I loaded my save only to discover that all the maps on my wall, as well as the duplicates I made of them in a chest nearby, had all frozen and would no longer update OR show the player marker. I am not sure why this happened. I remember an older bug where taking a map through the Nether would cause it to stop updating... and while I had just traveled to the Nether for the first time that same day, I was not carrying any of my maps with me.

Possibly related: Earlier that day, I had opened my level.dat file with NBTexplorer to change the allowCommands value to 1. I don't see why this would have affected the maps, but I don't know much about how the game code works. Regardless, the way I see it this is a bug.