[Edi]

There is no bug and no problem. Gaap happens to have the Berserker ability (+3) naturally, so there is no way to avoid it.

Units do not gain any special bonuses (such as berserking ability, magic resistances or anything else) from weapons that have been assigned to them with the #weapon command in the creation phase, or if you mod them to have some magical weapon. The only effects that will apply are the ones that are intrinsic to the weapon's attack, e.g. Flambeau as an intrinsic weapon still does 3x damage against undead and demons, but you do NOT get the fire resistance bonus because it is not a property of the weapon's attack, but rather a property of the magic item.

Edi