Version:            (using KDE KDE 3.5.8)
Installed from:    Debian testing/unstable Packages

verbatim copy from bugs.debian.org/451332:

"For a month or two now, I have noticed that if the active window I have 
in my xserver is a kmail message, and I switch out of GUI to a text 
console and then back to the GUI, the contents of my cut and paste
buffer end up being pasted in my email message.  This gets to be 
annoying after a while."

Reproducible not only in kmail but also kedit, kwriter ... and so on.

Just follow these steps:

1. Open any of those programs and keep it at top as an active window
2.- Write down something
3.- Copy to the X buffer by highlighting it

4-. Switch out of X to a TTY console
5.- Switch back to X

your X buffer is pasted ...

(not reproducible with GTK applications)