It may be a GMX Mail bug. I don't like the feeling of staying in KDE. (and KMail doesn't work) I won't switch to another email client until i could get back to GNOME (or, GTK+-based DE).
Well, as for top reply.. I remembered members discussed before and choosed top-reply. After new members joined, there are some members using bottom-reply.
PS: in fact, there are some broken characters in my eyes. :-(