Mob spawns in lit up areas

In my survival world, I built a house. I placed torches all inside of the house. There is a door and no entrances that aren't closed off, yet mobs still spawn in my storage room. I have only had spiders, skeletons, and creepers spawn in there but I made sure to check and make sure they didn't come through the door. I am now 100 percent positive that the mobs are spawning inside of a lit up room and not entering through the door. I'm not sure if this is just a glitch in my world or if it's happened to anyone else, but I hope it can change soon because I am not looking forward to the day that a creeper blows up my chests with baller loot in them.