When a model of a sphere is attached as a reference (viewed as a circle) using a reference presentation other than Wireframe, and then saved to DWG with visible edges merged, the resulting DWG displays the circle with hexagon/jagged like or straight edges, see image 1.
Image 1
Image 2
https://communities.bentley.com/products/microstation/w/microstation__wiki/8807/opening-and-saving-dwg-files-in-microstation-v8