I noticed this morning when I woke up that my server had crashed. Here are the relevant crash reports:

Original crash report from the server.

According to the user who was doing this: i was enchanting a pickaxe of the core at the exact moment shit went wrong, i was upgrading an unbreaking brick which looked kinda glitchy, and i think was doubled, so i was trying to upgrade it with itself??? (too late when i noticed that)

I attempted to replicate this myself by setting up an enchanting system and adding a number of pieces to a Pickaxe of the Core (from Thaumcraft). I suffered the following crashes:

Integrated server replication.log
Integrated client replication.log (possibly irrelevant)

I attempted to double-replicate it to ensure that this just wasn't a one off, although the error I got this time was an IndexOutOfBounds exception:

Integrated server.log
Integrated client.log

Unfortunately Gist decided to reverse everything.