When creating a new top-level folder (not a sub-folder of inbox), KMail is 
sending the wrong command to the IMAP server. This may be related to the 
namespace settings.

2 NAMESPACE
* NAMESPACE (("" "\\")) (("Other Users\\" "\\")) (("Public Folders\\" "\\"))
2 OK NAMESPACE completed

KMail sends this command:
3 CREATE "\\test"
which fails, because the server is expecting:
3 CREATE "test"

This does NOT affect Online IMAP: it sends the correct path. It also does not 
affect removing of folders in Disconnected IMAP. The correct command 
(DELETE "test") is sent.