Chunk is emmiting light, while there is no light close to it.

I have a feeling my chunk is corrupted, it always emmits light, nothing disappears after the server restarts in the chunk, but there is nothing that emmits light close to it. Can someone tell me, if it is not a bug that is, how to fix this? This has to be dark.

It was always light since I burned down a forest there. Most likely the fire was still going when the chunks got unloaded.

All this is on a non-modded minecraft vanilla server.