In strongholds, there can be light sources that do not produce light. This is not just visual, but physically. It can even let mobs spawn, when it is meant to be light level 8+. There can also be light when there is not meant to, like one of the pictures show.
Normally replacing the light source fixes it, however it is annoying.
(Sorry for any mistakes in this report, I have never reported a bug before)
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Duplicate of MC-142134