The light emitting air blocks were created in 14w30c but remain after updating the server to 14w31a.

The light emitted from the air block is block light level 15, and doesn't cause fire damage as if the fire had just gone invisible. When a block is placed in the glitched block the light disappears.

Ways to Replicate.
1. Burn down a forest (in our case swamp/birch)
2.Let the fire burn out.
3.Set time to night and look for light sources.