Version: 1.9.9 (using 3.5.9 "release 53.4" , openSUSE )
Compiler: Target: x86_64-suse-linux
OS: Linux (x86_64) release 184.108.40.206-0.1-default
folder properties has "show column" (default/sender/receiver)
RMB on colum header of mail headers opens "view columns"
toggle sender/rceiver does NOT show/hide the sender/receiver column, but toggles between sender and receiver.
This is no more reproducible on KDE 4.2 because the message list has been rewritten.
Think so too