Paint tool.... and the material schedule won't work?

This is weird.
I used the paint tool on a face of a structural concrete column, and applied a new material (named plaster).
Then something went wrong on my material takeoff schedule... the concrete volume of the column becomes 0. The plaster volume becomes equal to the column's volume. As if the entire column was made of plaster. But in the properties, the column's material is still concrete.
As far as i know, the paint tool shouldn't be able to change the structure of the column... so why my concrete volume becomes 0?

Even after the weekend, things aren't better.
After applying the paint tool, my material volume schedule doesn't work also for beams. Look the picture: the concrete volume of the Beam 2 is 0.
Maybe i have some wrong options set up... or maybe playing with the paint tool over structural elements isn't good for scheduling.

Check David Baldachinno's blog. We had a long conversation about that about a year ago and he ended up posting about it.

This one of the reasons we don't ever use the paint tool.
It gets worse if you split an elements surface, use the paint tool for different materials and then modify that element. You will lose the split segments and the materials painted on them.

If the columns are to be plastered and you need quantities for the plaster, make a plaster wall and model it. If you don't need quants for the plaster, give the column a plaster surface pattern.

You need to add the additional layer to the column for a sep. material. Painting is not the way to do what you want to do.