Import Font CP and UFO export

I’m not sure if it’s an expected behavior, but when exporting to UFO from a file using the ‘Import Font’ Custom Parameter, the generated UFO doesn’t include the imported glyphs. The Custom Parameter remains, but when you open the UFO, the glyphs seem to be missing and this error pop :

The linked font “MyFont.glyphs” has a different number of masters

The “imported” glyphs are not supposed to be in the .ufo. At least not as it is set up right now.

When you export to .ufo, it only contains one master. When you open that .ufo in Glyphs, the import parameter is still there but now the master count doesn’t match.

Why did you export to .ufo?

I know, but I don’t understand why imported glyphs are not supposed to be in .ufo.

I need to export .ufo to run some external script on files.