The Farming station consumes durability of unbreakable axe (Tinkers Construct).
I think the durability of an unbreakable axe shouldn't be consumed. The unbreakable attribute is gained by using reinforcement modifiers (5x) (Tinkers Construct).

• EnderIO: 1.10.2-3.1.157
• EnderCore: 1.10.2-0.4.1.62-beta
• Minecraft: 1.10.2
• Forge: 12.18.3.2202

you sure it's 5 times? does it actally say "UNBREAKABLE" in the lore?
AFAIK you need reinforced 10 to get UNBREAKABLE
or did that change from 1.7. to 1.10 ?

The farming station only tells the item that it should take damage. It is the item's job to either decrease its durability, energy storage, mana or do nothing.

Fair enough, strangely other machines (non-enderio) don't seem to have this problem.

To be sure I just looked it up:

if (type == ToolType.AXE) {
      tool.getItem().onBlockDestroyed(tool, worldObj, bs, bc, farmerJoe);
    }

So for axes, we don't even tell the item to take damage like we do foe hoes and shears (tool.damageItem(1, farmerJoe);) but only that is has been used to destroy a block. So it's all on the tool.

Thanks very much for taking the time to check.

oops, "invalid" was the wrong label. Your issue is valid, it's just not Ender IO's fault. (Unless boni can prove otherwise, I not that stubborn... ;) )

with you information i dug a bit deeper in the tool. You're quite right, it is an issue with the tool. If you use materials that are able to consume durability, ie. in exchange for a special ability, it will consume durability.
Again thank you very much for the assistance.