The ability to equip a musket is a feature still in development. The original game did not allow the player to equip a musket, but I found that many models supported the "musket" animation, so we added any model that supported the proper animation to select the "Equip" button. However, the models apparently still have a gun locator at the belt that still needs to be dealt with, so that musket will remain in the hands only. I suppose for the meantime, I should just remove the "Equip" button entirely for muskets, until that is figured out.
This only affects GOF 1.2 and ERAS, the other games still disallow musket equip for the player, as originally designed.