Q: Why do apple mail's folders not stay open after I drop a message in one?

I'm not sure, but have you tried opening another Message Viewer window in Mail to the folder you drag them to?

I don't use Apple Mail, but it would be normal for any mail client if you are viewing one list and dragging to another "folder" that the initial list stay the active list - even if you drag to a folder with SUBfolders, that parent folder might "spring open" to reveal the subfolders, then drop to a subfolder then the parent spring closed again, again the initial folder list remain active

Or am I totally missing your point?

• INBOX list
• drag to Funny
• remain on INBOX list