ItemEmptyMap line 29

mapdata.dimension = (byte)par2World.provider.dimensionId;

A map's saved dimension ID is downcast from an int, to a byte, then saved back to an int. For no apparent reason, which causes unwanted effects when mods are installed.

Basically this limits maps to working in no more than 256 dimensions.

I have attached some screenshots (using Mystcraft to get a dimension 256). Both maps are treated as being overworld maps even though I created the one in the Mystcraft dimension.

(I attempted to search this issue, but "map" shows up in basically every crash report ever, which makes it very difficult).