Dear Maintainer,

 As Bug#764982, backports is not enabled by default, but adding
 backports apt line with comment out is handy for users.

 Could you check attached patch, please?

Hideki Yamane <henrich@debian.org> (2015-05-18):

No need to tag "d-i" bug reports on packages that are part of d-i. ;)

I don't think that's a good idea. It's certainly OK for people who do
understand all pros and cons of having backports enabled to have
“backports” set here (be it by preseeding or by opting for an expert
installation), and to have uncommented backports line as a result.

Mraw,
KiBi.