[HexGirlBestGirl]

Adaptation has a bug. A simple bug, so i'll keep it short.

When offhanding a dagger, if you equip a weapon that your current class can use then switch to a class that cannot equip that weapon, you can bypass the need for adaptation entirely and still keep your weapon since it doesn't forcibly unequip your weapon. However, unequipping it and re-equipping it functions the same.

As an example.

Start as DH/MG, Gun Equipped, Dagger Offhand.
Switch to Monk/MG , Gun stays equipped even without adaptation. Dagger is still offhand.
Fight a fight. It won't get removed forcibly after.
Switch to Monk/Monk, Gun still equipped, dagger still offhand.
Remove the dagger for MMA, keep the gun.

With that, you're now a Mono-monk with your gun without allocating a single point into adaptation at all.
This can freely be done and your weapon won't forcibly unequip as long as you have the dagger offhand, thus i've concluded that it is the source of the problem. Likely due to the nature of being classless to equip.

Edit: Adaptation isn't what's bugged but rather the fact you can bypass it. I added this for clarity as for I reread it and see how it may mislead some.

[Neus]

You're sure you don't have ranks in talents that let you equip this?

[Miller]

I've tested it with them, as long as you're holding a dagger when you swap classes; you'll keep the weapon equipped that you don't have adaptation for, even if the class doesn't support it.