Error When Trying to Add Magic Quality to Transmuted Spiked Chain

[Stone Dog]

In the attached save, if I try to add a magic quality (via a 7th lvl dwarf's Weaponcraft talent) to the +3 spiked chain, I get an error (dump attached).

The action will cost 0 xp and 0 gp, and take 2 hours. Proceeding will add the desired quality just fine.

Of note is that the +3 spiked chain was a punching dagger, changed by an oil of transformation.

This does not happen if trying to add a quality to another weapon/armor (spiked chain included), not even on another weapon transmuted via oil of transformation (the save is set-up to test this).

Improving a plus on a weapon (even the one giving the error) works fine.

I don't know what happens if I try to add a second magic quality to the offending weapon, will report.

EDIT: for clarity, the error given is:

Error: ASSERT failed: 'XPCost > 0' in file \SRC\SKILLS.CPP, line 3481

[Stone Dog]

This gets weirder.

In the attached save, I've noticed that the +1 spiked chain will give the error if I try to add some qualities (e.g. numbing) but not others (e.g. vampiric).

And while no magical quality will result in the error on the +1 kite shield, every quality will result in it if I upgrade the shield to +2.

On top of that, if I upgrade the +3 chain (the one giving the error) a second time, I'll get no error.

PS: sorry for the many edits, posting as I test.

[Stone Dog]

I've just realized, bugged or not, magically improving a weapon doesn't take a skill check. Not sure if it's working as intended or not.