In the thread in which this was brought up, it was speculated that it had something to do with fixing the inverted luck influence on fireproof blankets being destroyed:

Digging out several levels of UD entirely without breaking a single pickaxe doesn't seem to be a luck-related thing, really. I did that in p14.

It's caused by the material of the pick axe. I need more information from Thomas to fix this. :)

I'm guessing that non-metal items can't be broken now due to 1698 and pickaxes are made of wood instead of iron?

Well, pick axes (currently) are neither made of metal or wood, so they don't break. ;)

Fixed (also fixed hatchet, wands and keys).

Just one question - how were they fixed? I have just broken (pre18) a pack of wands, and lost/broke few of keys during my gameplay, so it is not that they were unbreakable.

Would this mean that we will be able to repair pickaxes with Smithing?

They were added to a function that checks if items can be broken at all. This was used in more places than before (after fixing issue issue 1698) and items like the pick axe or hatchet were ignored, so they couldn't break.

So you are right that keys and wands could break before this bugfix, but for example they were never generated with "broken" status or couldn't break when reading a cursed scroll of repair.

No. Maybe you should create an RFE for this?