Blaze not spawning in nether / nether fortresses

[hellrazor]

Ah yes spawn egs, you can also right-click with a blaze spawn egg on the mob spawner and the pig will be changed to a blaze.
Thanks @NiLSPACE

Hey. Thanks, I can indeed manually spawn blazes now with blaze eggs.

I also managed to transform the pig spawner to a blaze spawner.
Still, I have the impression they are not spawned -> any idea?