[Kameron8]

When using Hare Kick or a few other special abilities, Twin Dance will not properly activate. Instead of attacking with your main weapon, then your sub weapon, the attack will take place twice with your main weapon. To replicate:

1. Equip Twin Dance and Verglas. Equip two fist weapons.
2. Go into Hare Stance, use Hare Kick. Conversely, go into Fox Stance, and use Fox Dive. Alternatively, go into Bear Stance and use Bear Palm.
3. Observe that you attack twice with the primary weapon.

I do not have a comprehensive list of what abilities behave in this manner, unfortunately.

[Neus]

This will need some more details, namely what weapons, does it occur with normal attacks or only these special attacks, etc.

[ThatOneHop]

I personally tested this out with both Fenri and Whulfs, since both had on hit effects. Replicating what Kameron says is it seems to only trigger the first weapon with the Verglas unique basic attacks and ignores the first. Fenri being mainhand only had it do the ice damage and not Whulf's light like it should, and vice versa. It might have something to do with how the unique basic attack is treated, perhaps?

[Kameron8]

I used fist weapons (Ymir for on-hit damage, in this instance) to test this. Basic attack and sub-attack do not experience this behavior, only the aforementioned special attacks. Stuff like Geldoren doesn't trigger the skill at all, so as far as I've been able to determine, it's only the Verglas abilities that cause repeating the primary weapon attack twice to occur.

[Neus]

This should be corrected, hopefully with nothing else broke.