Version: (using KDE 4.2.1) Installed from: Fedora RPMs If user has a message open in its own window and that same message has been deleted already, directly from message list for example - the message's own window delete function doesn't do anything anymore. If the message does exist, it deletes it *and* closes the window, which is logical. In kde3 kmail, this worked like user would expect, and thus should be fixed for kmail4 if possible. A tiny usability issue, nothing more.
Confirmed in KDE 4.3.5. Click on the button should close the window in my opinion.
I cannot reproduce this behaviour in the trunk version of KMail. It does affect the 1.13.5 version, but has since been fixed. In the trunk version, when the message is deleted from the message list, the message body disappears from the open window (although the message title remains as the window title) and the "Move to Trash" button now closes the window. I guess this bug must be marked fixed.
Thank you for taking the time to file a bug report. KMail2 was released in 2011, and the entire code base went through significant changes. We are currently in the process of porting to Qt5 and KF5. It is unlikely that these bugs are still valid in KMail2. We welcome you to try out KMail 2 with the KDE 4.14 release and give your feedback.