Probably its just me not understanding how TBC thinks.
Its 2 surfaces and i have choosen one to be original ground, that gives me cut and fill against the second surface.
In every section were this 2 surfaces don´t cross eachother the hatch for cut and fill is coloured nice but when they do cross (it will be a closed area) then its grey. I just figured out that the grey colour is "Sub Area". I changed it to another colour to check.
What is subarea? it should be cut or fill in that area. The area is also 0.00m2 but it should be more as you can see.

