Thunderbird Local Folder behaves like Drafts

I have set up archiving on Local Folders. However, when I double-click any email in the Local Folder, it opens as a draft. If I right click any email, the context menu has Edit Draft Message as the first option. I'm assuming this is the option that gets triggered on a double click. Subsequent options are Open in a new Tab, Open in a new Window and Open as a Conversation. I would have imagined that the last one should be the default option. I saw a backup of Drafts as one of the folders under Local Folders. I don't recall how/when I configured this, but I deleted it thinking it may have converted the whole of Local Folders into Drafts. But that has not helped either. Any pointers would be welcome. Thunderbird version info attached. Regards Thomas