Posting here as i think it's a bug with the select menu, /opt/debextra repository results not displayed, can only import directly using full package name.
Running dCore-jessie, created file named 01 in /opt/debextra containing:
http://ftp.debian.org/debian jessie-backports main
As per:
https://backports.debian.org/Instructions/#index1h2Repositories accessed:
* Using the repo
http://ftp.debian.org/debian jessie-backports main
* Using the repo
http://security.debian.org jessie main
A debinx.01 file gets created without error, contains lots of packages, interested in:
Package: openjdk-8-jre
Running sce-import -o openjdk just returns Jessie's default openjdk-7 import options, nothing openjdk-8 related,
but entering sce-import -o openjdk-8-jre appears to successfully import openjdk-8-jre.