Could you try to tar /var/lib/entropy/client/database/<arch>/sabayonlinux.org and upload the content somewhere?
After having backed up your current repo, could you try to run "FORCE_EAPI=2 equo update --force" and check again if you get openvz-sources pulled in?
It's a problem (perhaps) in old style virtuals. Joost, could you bump gentoo-sources in sabayonlinux.org, after user answered my questions? Current Gentoo profile sets sys-kernel/gentoo-sources as default virtual, if after having bumped gentoo-sources we get that as dep of "virtual/linux-sources", we would have to override gentoo default setting.
Keep me updated, I can fix this in my next coding session