Zombies and Creepers spawning "indoors" at light levels 8 and up.

I've noticed recently that I'm getting Zombies and Creepers spawning "indoors". I have an 11x7 structure 7 blocks high lit with torches at each end and on each wall at the halfway mark. There's a "loft" that's 5x7 that's lit with torches on both sides. I had a Creeper spawn inside on the main floor while I was standing in the loft. About 3 minutes later I was in another identically sized structure that I was in the process of building when a creeper spawned right in front of me, right next to a torch. I've noticed I regularly get zombies inside another structure that I'm not in a lot. I've been all over all of the structures watching the light level with F3 and there's nothing lower than 8 in any of them, and nothing lower than 10 in the ones where the creepers spawned. I'm not sure if this is regular behavior for creepers, but I was under the impression they shouldn't spawn in light over 7, and not two block away from a player.