February 2017 - last edited February 2017 by BryonyRae
Steps to recreate this issue:
1. Create a big enough room on the ground floor.
2. Add decks to the room by using the rounded deck tool.
3. Change those fences into full walls.
4. Switch to the 2nd floor.
5. Build a room on the 2nd floor.
6. Switch back to the ground floor, you will see the shadows.
Workaround:
You can simply break a wall to let the natural light in to eliminate the shadows. Then click redo button to get your wall back.
But the shadows respawn every time you load the lot.
I play vanilla game without mods/cc.
February 2017
This happens with me too, with windows and cabinets! there are so many bugs in this game
February 2017
Thank you for the detailed instructions @kinot9229. I was able to duplicate this glitch in game. Like in your final picture, not all decks have the shadows. It may depend upon the orientation of the lot. I will add this to our index of build mode bugs.