Spawner stops spawning after few mobs

Please make sure you kill the mobs that are spawned and then observe if more appeared. The mob count is limited in closed space, so if you have a certain amount of mobs there and they do not die or leave - your spawner will not spawn more.
Does the same occur on creative?

I got it tnx... BTW I have few more bugs to share...

If, at the time of spawning, 6 or more mobs of the spawner's type are present within a 9×9×9 area, centered on the spawner block, the spawner "poofs" without creating any mobs and then waits for the next cycle.

http://minecraft.gamepedia.com/Monster_Spawner#Mechanics