IMAP: Folders with sub folders cannot be deleted...

I am using em Client 6.0.2 or rather would like to use it as Outlook replacement (I have a rather old Outlook version).
I came upon a problem which also Outlook had: If you have an IMAP folder with a subfolder, it can’t be properly deleted, after sync it turns up again but the parant folder is greyed out and if you try on it even starts to duplicate somehow.

Deleting folders on the web client works without any glitch and deleting in em Client works properly, if you delete the subfolders first and then the parent folder. 

Something’s messed up there, Outlook has the same problem. As I am an IT pro and know how IMAP works I have some ideas what it could be, but maybe it’s a known problem??