I guess it's worth following up on the Avenger duplication bug.
For reference, the process is to equip Cecil with a Bow+Arrow setup.. Bow in the bad hand, arrow in the good hand.
In battle, remove the arrows from the good hand, and right afterwards, you select the Avenger and equip that on the bad hand.
Apparently, the game has poor code regarding 2-handed weaponry as you can perform this with other 2-handed weapons (such as the Poison Axe).
Then, you finish the battle.
Once you get out of battle, you will see a number right next to the right hand, signifying the bug was successfully performed.
In further testing, you can do the same for shields, by putting the bow in the good hand, and arrows in the bad. You would remove the arrows as normal and put the sword in the good hand.
Anyways, the issue is that the Avenger (via the aut0-Berserk effect) prevents the proper decrementing of the arrow removal. This is fixed in FF4ET for the duplication part.. not the bad 2-handed check part.