Comment 8 for bug 888665

No, no, I don't think it's inherently an issue with the version of apt - this code is all running within the build chroot, and uses the chroot's apt. When sbuild passes off the build-depends to apt, apt has no awareness of specific version requirements, so it pulls using the default source instead of looking to sources that are pinned lower.

Once apt has finished pulling from its default sources, sbuild goes back and says "Hey, you screwed up, I don't have a new enough version of whatever" and bails.