Looks like a DPI mismatch. I don’t know what resolution Luban issues. But that clearly the result of interpolating the information at different resolutions. The only way you’ll get desired results is to use SVG as the source.
What does the source SVG look like? You just can’t convert the BMP to SVG. You need to redraw the image as an SVG (vector) to get the result you desire. You can’t expect vector (high quality) results from bitmap (low quality) images.
I do not understand why the BMP files are not working…I had other more complicated BMP images imported fine and this image that is more simple is creating all sort of problems.
The BMP are working, you just have to understand how Luban (or any other graphics algorithm) rasterization works. Luban is set to interpolate pixels at X dpi, and if the lines in your original BMP are at the same multiple of X, you’ll get the non-regular result that you’re seeing. Nothing magical, just use a vector drawing tool to recreate your original image as an SVG.