Buried Treasure card doesn't allow Fusion as advertised

Buried Treasure is a new card in the Triassic set. It says, "Fusion: Conjure a Legendary card, and it costs 1 less."

Fusion is tooltip-defined as "Play a Zombie on this to use this ability."

The problem is that it will not allow me to play certain zombies on this item. My current hypothesis is that it's only allowing me to play Pirate class zombies on it, but that's difficult to test (playing game after game trying to get certain cards to come up at the same time).

And there's nothing in the update's Announcements section on Fusion that would suggest that Fusion cards only allow their own classes to be played on one another.

I've successfully used Fusion with cards other than Buried Treasure—at least in limited play of Triassic so far. Anyone else having this issue?