Mob Spawner will not stop

In my friend's server world, I was attempting to build a blaze farm, when I noticed I could not get the blazes to stop. Even after filling up every available spawning space with glowstone and stone, neither light nor lack of air space prevented the blazes from spawning. The same bug occurred with a zombie spawner on the same server. I do not know if anyone else on the server has discovered any other mob spawners, much less if they

I expected the blazes to stop spawning entirely.

What ended up happening was that the blazes would spawn inside the blocks of glowstone and cobblestone. They would take suffocation damage, but they would rise out of the blocks as soon as they saw me. The spawning rate seems in no way impaired. The only way I could stop the spawning was to turn the difficulty to peaceful, which felt like cheating.

I am not sure how to replicate the bug, as my single-player world doesn't demonstrate the same bug.