I go to combat with Muse and 4/4 token, op casts bury in books on my token after declared attackers and Muse trigger resolves. Before the Bury was cast I could cast the Heated debate in my hand but after it was cast I lost access to the discount provided by the Muse, I suspect that because the Bury is also reduced by 2 and somehow made the system think I had used my discount even though it was my opponent who cast the spell.

Needless to say, I lost a game I shouldn't have by being unable to cast my removal spell.