Not sure if this is considered a bug or a feature. If I have an existing font prefab with some symbols defined, and I then edit the text file for that font to change the character sequences for those symbols and reimport the font with the updated text file, my prefab remembers the old sequences in addition to learning the new ones. For now I'll just clear the old symbols out of the prefab manually, but it might be nice for the UIFont inspector to let me do this, or maybe even add new symbols.