After some time and various patches there's a new version of
xscreensaver that fixes a lot of issues with 5.05 and XineRama. Thanks to all that submitted patches: Bas Zoetekouw, Vincent Crevot, Lionel Elie Mamane and Daniel Dickinson for the desktop file.
deb files are available here along with the dsc, changes, diff.gz and orig.tar.gz files. If you don't use
i386 then do:
dget --build \ http://debian.rivco.info/xscreensaver/5.05-3/xscreensaver_5.05-3.dsc