Cavern of souls and tribal cards.

[pryite199]

This came up recently on MTGO a player Tapped a Cavern of Souls to cast Tarfire and it un-counterable. Is this a bug of the software or does the fact that Tarfire is a tribal card allow for it to behave as a creature?

[Esper3k]

This should be a bug because Cavern of Souls specifically specifies Creature spell (Tribal does not automatically make a card a creature spell).