Black dragons and magic immunity

[Pug of Stardock]

I thought black dragons were supposed to be immune to magic. I just fought a mini-boss who cast the geyser spell and my black dragons went floating up with the other units affected. Didn't do much damage, but the dragons were affected.

I know the description for black dragons in WoTN says 80%, but so many of the descriptions in the game are cryptic or outright wrong, I wasn't sure what to make of it. In Armored Princess, I NEVER had blackies affected by spells - mine or others. I have NEVER been able to use one of my spells/buffs on my Black dragons in WoTN, so I was surprised when this happened.

Did this immunity change in WoTN? Bug or feature?