Version:           1.9.1 (using KDE 3.5.1, Gentoo)
Compiler:          gcc version 3.4.4 (Gentoo Hardened 3.4.4-r1, ssp-3.4.4-1.0, pie-8.7.8)
OS:                Linux (ppc) release 2.6.14-hardened-r5

This minor problem has been present in Kmail for a long time (I'm thinking at least a year, since I've been running a UTF-8 system for at least that long), but I only recently figured out exactly how to make it happen.

In the "message list" pane, when a message subject or sender that is not yet visible contains Unicode text that has not been rendered yet, clicking the scrollbar to move down the list will cause it to scroll down TWO "pages" instead of one.  I'll clarify with an example:

I'm looking at my Spam folder on an IMAP server.  This folder contains junk mail in many languages.  :)  Since I've just started Kmail and am looking at this folder for the first time today, it's at the very top of the list.  All of the messages displayed (10, since my list pane is rather small) are in English, but the 15th new message (which I can't see at the moment) is in Japanese.  Clicking once on the scrollbar to move down the list, I see the scrollbar move, there is a noticeable pause while KDE deals with the Japanese characters, then the scrollbar moves again and I am now looking at messages 21--29.  I have to scroll UP to see message 15.

Scrolling up or down past more messages in Japanese works as expected, but now if I have some spam in Korean (different Unicode block, or whatever the proper term is) the double-scroll will happen again when that one should come into view.

Closing Kmail and starting it again will cause the double-scroll again, the first time a message with "interesting" characters in the header should be scrolled into view.

Loaded plugins/backtraces:  N/A
How to reproduce:  See above :)
Expected behavior:  Kmail should only scroll down one "page" of messages in the list, even if these messages use Japanese, Korean, Hebrew or whatever in this pane.  On a fast system (which mine is not), the user might not notice the double-scroll and therefore miss seeing some messages.