Synchronization leads to duplication & submitting patches

Some images in the media library aren’t listed by Media Library Folders. If I sync, duplicates get added to the Media Library (the originals don’t show up in Media Library Folders).

I don’t have enough info right now to write a complete bug report. I hope to dig in further and see if I can produce a patch. Would a patch be welcome? What’s the process for submitting a patch?