ToME: the Tales of Maj'Eyal

On 115 I just reached my vault and retrieved a few mindstar items from there. Nexus of the way worked nicely but Core of the Forge made errors whenever I would hit an enemy.

The errors (that I reported) seemed to have something about on-hit effects. Core does have a damage type of 'leaves' which I've never seen before.

Is Core of the Forge an add-on item cause if it is then that might be a reason for the bug as I don't currently have any add-ons installed.

Core of the Forge is not an addon , it's part of the default artifacts list :
http://te4.org/wiki/Artifact

So maybe it's one of those effect errors, like the ones that affect some of the dagger artifacts that generate errors on hits sometime.

What game version did the Core in your vault come from?

^That could be to blame. The item deals a special damage type that may have changed slightly between versions, causing errors.

Can't remember for certain but I'm pretty sure it was 1.0.5 or 4. After 5 I went straight to 1.1.3 which is like 1% chance it came from.