Followup on this issue: The sources.list file in /target/etc/apt appear to be different when performing installation preseeded or manual. It appears that the sources.list file generated with the preseed method has forgotten to add the mirror settings and the updates section of apt. It is generated correctly in the manual case.
$ diff 796941-file-preseed_targetEtcAptSources.list 796941-file-manual_targetEtcAptSources.list 1,2d0 < # < 6a5,7 > deb http://ftp.belnet.be/debian/ jessie main > deb-src http://ftp.belnet.be/debian/ jessie main > 9a11,13 > # jessie-updates, previously known as 'volatile' > deb http://ftp.belnet.be/debian/ jessie-updates main > deb-src http://ftp.belnet.be/debian/ jessie-updates main
# deb cdrom:[Debian GNU/Linux 8.1.0 _Jessie_ - Official amd64 NETINST Binary-1 20150606-14:16]/ jessie main deb cdrom:[Debian GNU/Linux 8.1.0 _Jessie_ - Official amd64 NETINST Binary-1 20150606-14:16]/ jessie main deb http://ftp.belnet.be/debian/ jessie main deb-src http://ftp.belnet.be/debian/ jessie main deb http://security.debian.org/ jessie/updates main deb-src http://security.debian.org/ jessie/updates main # jessie-updates, previously known as 'volatile' deb http://ftp.belnet.be/debian/ jessie-updates main deb-src http://ftp.belnet.be/debian/ jessie-updates main
# # deb cdrom:[Debian GNU/Linux 8.1.0 _Jessie_ - Official amd64 NETINST Binary-1 20150606-14:16]/ jessie main deb cdrom:[Debian GNU/Linux 8.1.0 _Jessie_ - Official amd64 NETINST Binary-1 20150606-14:16]/ jessie main deb http://security.debian.org/ jessie/updates main deb-src http://security.debian.org/ jessie/updates main
