Stonebound Pickaxe Weirdness?

[woggy]

I noticed an odd thing upon levelling my pickaxe - it's displaying a weird name in the tooltip, and I'm not sure whether it's actually applying the Stonebound effect at all.

I went digging into the NBT data, and instead of seeing a change to Shoddy like I'd expect from a tool that had stonebound effects, it's got an extra Boolean for Stonebound. Is this a bug, or is the Stonebound from levelling up supposed to work differently from the one gained from innate tool components?

My steel pickaxe

and here's a freshly crafted Ardite pickaxe I made in a Creative world, with the NBT data I was expecting:

TCon 1.8.8, Iguana 2.1.6, TiCTooltips 1.2.5, all for Minecraft 1.7.10.