I'm building a new building. I made the floor plan and planted a lamp at each tile junction that will have a wall. I then planned and built the walls of the first (ground) floor.
Next I made the floors above around the outside walls and also 2 staircases to get up to the 2nd floor.
I then planted lamps around the perimeter of the 2nd floor and called it a day.
When I logged on the next day, the lamps along the 2nd floor south wall had fallen through to the ground floor and were not accessible except for the two that were at corners.
The south wall is towards the ships. Notice there are no lamps on the 2nd floor there.
You can see how I plant the lamps before planning the walls and how the planned walls look with the planted lamps.
So, what I did was...
1. Prepare the groundplan of the building.
2. Planted lamps around the perimeter of where the outside walls would be.
3. Planned the 1st (ground) floor.
4. Built the walls of the 1st floor.
5. Planned the floors above around the perimeter and the internal walls for the 1st floor.
6. Built the floors above.
7. Planned and built floors below for the staircases (4)
8. Planned the staircases and built 2 of them to get to the 2nd floor.
9. Planted lamps around the perimeter walls of the 2nd floor.
10. Logged for the night.
11. Returned the next day and found that the lamps on the 2nd floor south wall had disappeared! None other, just those.
12. After examining the 1st floor walls I discovered that there were 2 lamps at each of the corners of the south wall. It followed that the others were in the walls but I could not detect them to retrieve them.
What I expected was for everything to be where I had put it.
The above steps may, or may not, reproduce the problem. Since I have an additional 5 - 7 floors to build it would be nice to figure this out beforehand.
Thanks for your efforts