I use cropping mask often to replace items in older videos.
When I use a positive mask and same mask but negative I get a border. The positive mask covers a rectangular area and the negative everything else. It's the same saved mask.
How do I fix it? I tried different feathering options to no avail. My video is simple text & solid color background in all videos (just instructional videos).
The only laborious workaround is to create both mask by hand and enter exact y,x positions to the mask corners.