Leon as reported since few weeks the shadow problem with the doors. I know this issue since the beginning. In fact, I'm not pro for lighthing under Source. The original door use a prop for that and are linked with a hidden func_door.
The best solution at this time is remove the prop and use the func_door with texture for the door. This thing solve the problem of dark door when is opened. I can dot it on all doors already added without big change (remove prop, change size of func_door and add texture).
Look this video for see the difference between the old and new door.
You like the old door or the new ? Please comment it.