Just experienced bug in arena and confirmed doing to a solo setup.
Athletic studies gives a 1 mana discount on next rush minion. If used on Imprisoned Vilefiend, the minion gets the discount from 2 mana to 1, goes dormant and the 1 mana rush discount from athletic studies remains in effect for another rush minion. I was able to play another discounted 1 mana Imprisoned Vilefiend and then a discounted 3 mana Hippogrpyh.
Some sort of bug between the discount and dormant functions.