So if the map is not saved, an old version is run.Editor.log wrote:Warning: Can't save D:\tmp\MyMap.unr: Graph is linked to external private object Texture Engine.SmallFont.Texture0
Of course it it easy to fix this problem by Tools > Replace Texture or by Export T3D -> Edit -> Import T3D, but for an none experienced mapper it might be a unsolvable puzzle, especially if the Texture is not visible.
EDIT: Ahh, stupid me. As soon you have set this texture, you cannot save the map. So this map can only exist in memory, not on disk.