"Open Below"-What's up with the Roof?

[MCK]

I am using Home Designer Suite 7.09 and have developed a 1 1/2 story home plan.

I added a rectangle of invisible walls to accomodate the stair system and chose "open below". I also checked "ceiling" and "roof" above this room. The opening was created without a flaw except now I have a hole in the roof that matches the opening. Why? How do I correct my error?

I then tried to create an opening in the main floor to match the loft and although I re-created the rectangle and chose "open below" for this area the program did not create the opening. I reworked my effort several times trying different options, ie no floor material, etc., and hours later still could not create an opening in the main floor. The floor material is still quite visible in the "open below" area. Please provide me some suggestions.

I am aware I am not doing something correctly but I have read the tutorial and I am still obviously missing something. Thank you in advance.