Spiders suffocating when spawned by dispensers

So I have made a "mob fighting" world, where my friends can fight mobs and exhange their loot for rewards. The world has different "chambers" each containing mobs to fight.

However, I have a problem with one of these, and that is the Spider chamber.

Each chamber is set up so that at the press of a button, dispensers spawn mobs to fight. However, because the dispensers are placed in the wall, for some reason Spiders immediately start to suffocate when they are spawned.

I have tried spawning Spiders from wall dispensers in MCPE 1.1.5 and it works just fine.