This isn't exactly a bug. It's how the lighting engine works. Idk if turning on shadows would solve this issue, but essentially light is applied to an object as if it is the only object there. Lights on one entity do not land on other entities. That door is treating the ambient sunlight as if there were no other structures to alter the light in the first place.
And on the triangular wides of wedges in some orientations.It is reported as a bug ... this will even work if you fully enclose the entity in a dark box ... it will be illuminated by the sun without the light beeing blocked. So yes ... a bug or better an inability by the lighting system.
There are more problems with lighting on corners or on the borders of chunks that have to be fixed in the future.