[thejeff]

I'd say it's a bug.

It still can be worth it though. Particularly early game when people aren't likely to dispel it right away. Or if you can convince people that you overcast it so they put a ton of gems into taking it down.

With the gem producers, it's a trade off on how long it takes to pay back. That gets worse if you throw more gems in to protect it and better if you cast it at a discount.

And in some games you could cast Arcane Nexus at 80% base cost and make more than that the turn it goes up, then recast it next turn.