Just in case: Try changing the encoding: Menu "View" ("Widok?") ->
"Set Encoding", then select the encoding used by your correspondent (or try other encoding used in Poland), BEFORE clicking on "Reply"…
Thanks Patrick. I have utf-8 set as my encoding and changing it to other values (iso-8859-2) does not help. Moreover, I do not havu this problem on openSuse with KDE3, so this looks like Trinity's regression.
Jan