I have attached two pictures to this report. Both pictures were taken inside the same corridor, where the floor consists of slabs (top) and the stairs leading down from the consist of normal stairs. The lighting issues occur when there are no solid blocks behind slabs and stairs and the sun has an indirect line to them. The sunlight somehow gets trough the corners, which I believe is unintentional. To prevent this, the player is forced to place solid blocks behind the slabs and stairs to block the sunlight.

It's also important to note that I did not have any shaders on during the time of this screenshot that might've caused the visual issues, but everything was set on default. This issue should be easy to replicate by constructing a dark room with the floor consisting of slabs, and having no blocks around the slabs that would stop sunlight.