If you are talking about keeping a perfect circle from distorting after rotation, then on the Attribute tab (after clicking the blue Options button on far right) select the "Distort Clip" option. Then over in the preview window, right-click and select "Keep Aspect Ratio" from the pop-up menu. If that doesn't work then maybe one of the other options on the pop-up menu will correct the distortion.
The other option you may have to test is the "Perform non-square pixel rendering" option in the project settings (and share settings). Depending on the project dimensions, that can distort an image. It's sort of equivalent to selecting Keep Aspect Ratio or Fit to Screen (project dimensions).
MotionStudio 3D 1.0; Corel VideoStudio Pro 220.127.116.11 (Ultimate)(Discs), Corel PaintShop Pro 18.104.22.168 (Download)