Open below floor issue

[Phil_C]

Hello All
I have a house plan with five floors. The first two floors are living areas, the third floor is the attic and fourth and fifth floors are access to an observation tower. On the third floor I have a small room for the stair well that is set to "Open Below". On the rest of the floors the view in "Perspective" "Floor overview" shows the stair way to the floor below correctly but on the third floor it shows a white plane instead. The top of the floor is removed correctly but what appears to be the ceiling of the room below is not removed. I have tried deleting the walls and redrawing them but to no avail. I also checked the defaults for each floor and I could not see anything different. Does anybody know what could be the problem?


Regards

Phil