Polyline displaying as chords on early reads of external DWG

Hello

     This feels a bit like a bug - when I open a DWG (or DXF) created elsewhere, polylines display as a series of chords, typically 2 or 3 per quadrant. Every time I save (no changes) then reopen, the polyline gets better, showing one or more extra chords per quadrant each time.

     I can speed up this process by exploding one polyline, then undoing the explode. After save and read the polylines look almost (but not quite) perfect - I have to zoom in a long way to see the chords. Just doing this to one polyline affects the display of all polylines on next open.

     Is there a process for reporting bugs?

Thanks