Blaze Spawners continue spawning blaze no matter how high the light levels are

When in range of a blaze spawner it will continue spawning blaze even when the spawning area is lit up by lava.

My blaze farm used to turn off when i turned the lava on now blaze just continue to spawn.. they also seem to be spawning outside the spawning area as the area around the farm gets full of blaze after a short time of being in range of the spawner. It also causes quite a lot of lag and unless I turn my render distance down to the minimum the game is unplayable around the blaze spawner.

Cheers