DanoCAD

I have this two-story stair well with floor to ceiling windows on two adjacent corner walls and one of the windows has this piece of what appears to be subflooring showing and I cant figure out why it is there. The other window does not have it . . . it is on a "flooring surface" layer . . The second story walls are lined up right on the money. Yet I still see this piece of flooring running right through only one of the windows . . .