[Minecraft FTB Monster] Exploding Creepers with MFR Grinder?

[Heart]

Hello,

I am currently working on a Mob Grinder, using the MineFactory Reloaded Grinder, and 3 Spawners(2 From a Thaumcraft Dungeon, 1 From Roguelike Dungeons), and a few fans from OpenBlocks.
However, it seems that the Creepers spawned from the Creeper Spawner explode randomly,
which destroys the itemduct next to the grinder.
I have no idea, what's causing this, so I built obsidian around the itemduct to protect it, but this also doesn't seem to work.
There aren't any other damages caused by the explosion, so I guess it could also just be the itemduct exploding by itself randomly.

Does anyone have any idea, why this is happening?

Pictures:

 

[loboca]

The general reason creepers blow up in grinders is White Mages from Ars Magica 2 attacking them when they spawn. If AM2 isn't in Monster, I dunno.