Version: (using KDE KDE 3.5.6) Installed from: SuSE RPMs Make sure you have several entries in Klipper history. Run Kmail. You should see a mail in preview pane. Ctrl+a. Ctrl+c. Reply. The whole mail is being replied, including header. Cancel. Quit KMail, run KMail again. Ctrl+a, ctrl+c. Open Klipper history. Choose some entry. The selection in KMail has gone. Reply. The header is included (bug).
This is not about klipper and is neither a bug. The fact that the klipper selection removes the selection in kmail is the fact that a further reply just replies to the whole mail as usual. You might not know that reply in kmail has the feature that only selected text is included in the mail body if you hit reply after selecting some text.