This bug only affects the sketons since they got their new Ai.
While idle, skeletons hide under shadows fine.
In old versions of the game, they would start shooting the player without leaving the shadows and wouldnt follow if the player fleed. However, now they will strafe while shooting and always will leave the safety of the dark to start burning, run back for cover, engage player again (and walk in direct sunlight again), hide etc. and they will quickly get themselves killed.