startkde deletes custom plasma-desktop.desktop file

I use a customised configuration for running KDE. In particular, I use fvwm as the window manager, and disable plasma-desktop by creating my own plasma-desktop.desktop file in ~/.config/autostart, which is just a copy of the one in /usr/share/autostart with "Hidden=true" added to it.

On earlier versions of Ubuntu (up to natty, at least) this had the effect I wanted: plasma-desktop would not start up, and I could use fvwm's desktop furniture instead.

I'm now re-creating this setup on a precise (12.04 LTS) install, and find that plasma-desktop not only starts when I thought I'd disabled it, but somehow, my plasma-desktop.desktop file is deleted. A bit of digging reveals the problem to be lines 381--400 of /usr/bin/startkde (from kde-workspace-bin 4:4.8.2a-0ubuntu4).

# Added by Debian to fix bug #584905.
# Reset user plasma-desktop/plasma-netbook autostart configuration if autostart
# desktop file is not available system-wide for either of the shells. This
# ensures that a user does not end up without any autostarted plasma shell when
# a package of the active shell gets removed.
if [ ! -e "/usr/share/autostart/plasma-desktop.desktop" ] && \
   [ -e "/usr/share/autostart/plasma-netbook.desktop" ];
then
    # Reset custom plasma-netbook configuration
    user_autostart_dir=`kde4-config --path autostart | cut -d: -f1`
    rm -f "$user_autostart_dir/plasma-netbook.desktop"
elif [ -e "/usr/share/autostart/plasma-desktop.desktop" ] && \
     [ ! -e "/usr/share/autostart/plasma-netbook.desktop" ];
then
    # Reset custom plasma-desktop configuration
    user_autostart_dir=`kde4-config --path autostart | cut -d: -f1`
    rm -f "$user_autostart_dir/plasma-desktop.desktop"
fi

I haven't taken the time to understand the issue that these lines were trying to solve. But deleting the user's config is definitely not an okay way to fix it. Please could someone take a look and invent an alternative fix that doesn't clobber my settings?

Thanks.

Stephen