Bug#409925: i see something like that
i'm not using kdesktop (instead olvwm) and i just upgraded to unstable,
and when i started kmail it showed only the welcome screen ;
clicking on it or on any of it's links didn't change that ;
the menu did work.
So i couldn't see anything, until i selected 'find message'
upon which it popped up a list and i clicked on a random entry.
This made it show messageslist, but not folders ;
the messagelist had some extremely old mails in them,
i don't know where it found them, but not in ~/Mail .
Later i discovered an iconified something that showed a kmail menu when clicked on,
i killed it before i found out what it was.
(maybe not a composer window ; i wouldn't know why it would pop that up at startup).
After i had killed the iconified thingy (it had a minuscule icon),
i got a password popup asking on behalf of kmail to unlock my kwallet.
i filled it in, and it disappeared.
Now i restarted kmail, and it looks normal,
all folders present, correct number of unread messages, trash emptied,