Don't make a spawner in Minecraft out of stone. Use something like cobble instead.

Why? Because Endermen steal stone.

I have a spawner in my ATM9 world that I made a part out of stone. I got to my spawner and was wondering why it stopped (using special dirt that spawns mobs constantly). I saw there was some light in the enclosure (this disables spawns). Noticed 3 stones missing near the bottom below the dark windows. Found that stolen stone in the mob grinder storage. Replaced with polished granite.

Can't have shit in this neighborhood.

I did have a moment of silence for the Endermen who tried to save their brethren from certain doom. Brave warriors who died for the futile cause.