It might be caused by an over-aggressive application of a noise reduction filter. Or maybe a destructive deinterlacing filter is blending the fields together. Take some time to explore all the settings in the application, so you understand what's happening to the video.
To fit on a single layer DVDR, the bitrate should be somewhere between 4 and 5 Mbps (best to calculate the exact target size you want to aim for, to make maximum use of available space). VBR should give better results than CBR.