Wakazashi

[Bunny]

Cannot equip in main hand. Must dual wield then remove main hand weapon to wield in main hand.

cannot adjust appearance. Once its in the main hand, and appearance adjustments fail and the weapon reappears in inventory

Iron wakazashi has a lvl 16 restriction

[Twily]

Wakizashi:
Base Damage: 1d6
Base Critical Threat: 19-20/x2
Base Damage Type: Piercing
Weapon Size: Small
Feats Required: Exotic or Monk\nSpecial: Grants Shield AC Only Equippable in Off-hand

The above quote is from the update thread.
I think being able to equip it in your main hand at all is a bug.