Version:           1.6.2 (using KDE KDE 3.2.2)
Installed from:    SuSE RPMs
OS:                Linux

This is how you trigger a counterintuitive layout of the display of e-mails in kmail:

1) Use the field in which e-mail text and attachment are normally displayed to only show the attachments (by moving the separation bar between e-mail text and attachment to either top or bottom of the field, respectively).

1.5) Wait some time to forget what you have done. This will enhance the effect of the following step ;-)

2) The choose an e-mail without attachment.

Now, from a programmers perspective it might be natural that no e-mail text is displayed in the field; it is grayed. There is also no separation bar displayed, since there is no attachment to be separated from the e-mail text.

However, as a user my heartbeat quickend, since I thought that all of my e-mail files were corrupted and could no longer be interpreted and displayed correctly. Furthermore, in such a situation there is no simple and obvious way to display the text of the e-mail. The separation bar is gone to change the size of the e-mail text kmail should display. Even a doubleclick (to open an e-mail in a new window) shows only a grayed field instead of the e-mail text in a new window.
In order to see the e-mail text of such an e-mail, I had to select an e-mail with an attachment again, revert step (1) and find the e-mail without attachment again.

I admit that after analysing the situation, the solution sketched above is quite obvious. But I would like to see no other user entering this trap.

A possible way to prevent such a situation might be to treat the "attachment-window" as a child window of the "display-e-mail-text-and-attachment-window". If 100% of the  display-e-mail-text-and-attachment-window is currently used to display the attachment and an e-mail without attachment is selected, then the display-e-mail-text-and-attachment-window should only show the text of the e-mail.