Peculiar issue...block harvesting errors

Hello,

I've set up a tool enum that looks like this:

public static EnumToolMaterial COPPER = EnumHelper.addToolMaterial("COPPER", 1, 250, 3.5F, 0, 5);

It's not able to harvest diamond, obviously. However, it is able to harvest a block STRONGER than diamond.

MinecraftForge.setBlockHarvestLevel(blockCobaltOre, "pickaxe", 10);

Basic diamond pickaxes aren't able to harvest this ore, but my copper one can. Halp?

-Blf