What is the bug?

I have a GeoTIFF RGB raster which uses the color 255,255,252 around the edges (without defining it as nodata in the file). I want to translate this to a GeoPackage with this color transparent using an alpha band. I have been using gdalwarp with the combination of -srcnodata "255 255 252" -dstalpha to successfully accomplish this.

With the new CLI, as far as I can see, the equivalent is gdal raster mosaic. I am not able to accomplish the same result however. Instead of creating an alpha band where the specified color is transparent, the color is defined as "Nodata" in the gpkg_metadata table (which does not make sense as RGB GeoPackages does not support the concept on Nodata according to the format documentation )

Steps to reproduce the issue

Old gdalwarp command with correct result:
gdalwarp -f gpkg -dstalpha -srcnodata "255 255 252" rgb_raster.tif gdalwarp_output.gpkg

New CLI with incorrect output:
gdal raster mosaic --of gpkg --add-alpha --src-nodata "255,255,252" --dst-nodata 0,0,0 rgb_raster.tif gdalmosaic_output.gpkg

Versions and provenance

Windows 11
GDAL 3.11.0 from conda-forge

Additional context

No response