Slagmaw not counting down

Slagmaw had 5 turns remaining, I had a Bloodrock Co. Shovel equipped, and a Tirion Fordring in play. My opponent killed my Tirion on their turn, which equipped the Ashbringer, destroying my shovel, causing me to excavate. On my next turn, Slagmaw should have counted down to 2, but he did not go down by 2 turns when the shovel excavated me on my opponent’s turn.