OK, I've found out the bug, it is inside kio_man.
It affects only distributions which do NOT use mandb, like RHEL.
It is originating in an Ubuntu-provided patch:
http://old.nabble.com/Bug-449554%3A-konqueror%3A-Recode-manual-pages-to-UTF…
I've reverted the faulty patch and created TDE bug 714:
http://bugs.trinitydesktop.org/show_bug.cgi?id=714
It has solved the problem on RHEL 5 and RHEL 6.
I will upload the new RHEL kdebase packages soon (3.5.13-9).
Francois Andriot