So when I attempt to add new custom ore mixes in the WorldGeneration config and run the game it resets the values I entered.
This is what happens to the first and second custom ore mix slot entries: http://pastebin.com/xmtbFGQ7
You can see how it overwrites the data in the slot with the default values and leaves behind what I entered.
It also does the same to the line that enables the ore mix near the top of the config but it adds _false = false http://pastebin.com/YHpD0udY