Just stumbled upon this bug-report, that exactly described a problem I had for some time with kmail + imap on my “web.de”-account
http://bugs.kde.org/show_bug.cgi?id=153284
The proposed solution worked fine for me, so no more hanging inbox, fyi what to edit and where:

Despite being unintuitive, you have to use the edit-icon, changing the input field directly will result in kmail ignoring your input when you re-enter the form.
btw: this is my first post using bilbo/blogilo
EDIT: for further explanation – the value in “personal namespace” before was set to “<empty>” and I changed it to “inbox.” (don’t miss the dot at the end). This bug only appeared for me, when entering the inbox, not when opening any other imap-folder plus it only happened on this account, two other accounts I have are not affected, probably because with those two the automatic namespace estimation works.

Thanks a lot.
I do not know why i had suddenly that INBOX. stuff in there…
At first i thought i could just remove the text in the textboxes – which does not work. It is important to use that button to remove that Inboxes.
I’ll give this a try, thanks for the tip! Really tho, without the “EDIT: for further explanation” part, the whole post is rather unclear.
More good stuff!
It is an fascinating idea… I believe that you may upgrade it.