Spawner Flame Remaining

I was in the Nether, in a Nether Fortress, I found a blaze spawner. I fought some blaze to get blaze rods, then broke the spawner with a diamond pickaxe, enchanted with eff. 4 unbreaking 3 fortune 3 (guess).

What I thought was going to happen:
I mined the spawner, got xp, and left.

What actually happened:
I got XP, and the spawner successfully broke, but the flames inside remained.

Upon leaving and reentering the Nether, the flames disappeared.