Weird situation with surfaces

Today im filled with problems guys haha, im going crazy.
I have this DC i have made long ago and it neves has gave me any problem, today, all of the sudden, if i change anything, even the smallest attribute, it changes its shape from a circular tube to a polygon, i show you the picture, im going really nuts because it makes no sense, even happens with the DC i ve made using this DC, i have not change anything! Help:_