Are you removing KDE? The package knx-installer gets removed if you remove KDE because it depends on kdelibs4 which gets removed when you remove KDE by doing 'apt-get libarts1' to trash kde. I had this happen also.
Perhaps you can do 'apt-get install knx-installer' after removing kde? I'm trying a different route, upgrading kde bit-by-bit instead of removing & reinstalling all at once. I'm remastering knx 3.3, removing what I dont want & upgrade to KDE3.2. Maybe I should just start from knx 3.4....