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.
Related issues
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Related to MC-2497 ?
I found this problem when using world edit/ voxel sniper in mp and single player. Unfortunately I wouldn't know how to fix it

Does this still occur in 1.4.5?
No. This was fixed in 1.4.5
I had this happen with a zombie spawner in the overworld as well.