same item has different stats

https://imgur.com/a/pOZU0

I have created a char and gave her weapon profiency warhammer. I gained the item on the left side and equipped it.

Then I went to the area northwest of town, defeated the first enemy group, took the path upwards and defeated another group of enemies.

One of the lagufaeth dropped the weapon on the right side.

The weapon dropped by the enemy does not have the +1penetration although it is written in the description.

expected behaviour:

- Items with the same name should have the same stats or produce the same effect.

- Things that are written in the description should really be on the item.

update:

I have switched the weapons and the effect switched.

The equipped weapon always has the bonus penetration and the unequipped weapon never has it.

The bonus penetration is not shown on all unequipped weapons.

expected behaviour:

Items that can be equipped should always have the same stats, no matter if they are equipped or not.