In version 4:4.5~20100910.1175630-1maemo6.1174786 , sometimes when deleting emails from an imap resource, the application crashes. No further information collected yet.
Console output probably not helpful ("KCrash: Application 'kmail-mobile crashing...'). However, I believe that I have found a way to reproduce: Open a mail, but click on the "back to list" button before the mail was laoded (i.e. the screen still shows white only). Then attempt to delete that mail.
*** This bug has been marked as a duplicate of bug 251378 ***