Bug#856657: gnome-software: Sometimes claims repo is not active

[Marcus Lundblad]

Package: gnome-software
Version: 3.22.5-1
Severity: normal

Dear Maintainer,

For some apps, when I try to install it (on Stretch), I get a dialog claiming
that the repo "debian-testing-main" needs to be activated.
Clicking "Activate and install" brings up a password prompt,
but then I get a dialog showing an error message (from apt I guess)
saying: "E: Could not find the repository"
But some apps install fine.
One thing I noticed, the ones failing seems to indicate "Download size" in the
UI, whereas the working one don't.

Example of non-installable: Milkytracker
Example of installable: Rosegarden

-- System Information:
Debian Release: 9.0
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=sv_SE.utf8, LC_CTYPE=sv_SE.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages gnome-software depends on:
ii  appstream                                    0.10.6-1
ii  dconf-gsettings-backend [gsettings-backend]  0.26.0-2+b1
ii  gnome-software-common                        3.22.5-1
ii  gsettings-desktop-schemas                    3.22.0-1
ii  libappstream-glib8                           0.6.8-1
ii  libatk1.0-0                                  2.22.0-1
ii  libc6                                        2.24-9
ii  libcairo-gobject2                            1.14.8-1
ii  libcairo2                                    1.14.8-1
ii  libenchant1c2a                               1.6.0-11+b1
ii  libfwupd1                                    0.7.4-2
ii  libgdk-pixbuf2.0-0                           2.36.5-2
ii  libglib2.0-0                                 2.50.3-1
ii  libgnome-desktop-3-12                        3.22.2-1
ii  libgtk-3-0                                   3.22.8-1
ii  libgtkspell3-3-0                             3.0.9-1
ii  libgudev-1.0-0                               230-3
ii  libjson-glib-1.0-0                           1.2.2-1+b1
ii  libpackagekit-glib2-18                       1.1.5-1
ii  libpango-1.0-0                               1.40.3-3
ii  libpangocairo-1.0-0                          1.40.3-3
ii  libpolkit-gobject-1-0                        0.105-17
ii  libsecret-1-0                                0.18.5-2
ii  libsoup2.4-1                                 2.56.0-2
ii  libsqlite3-0                                 3.16.2-2
ii  packagekit                                   1.1.5-1
ii  software-properties-gtk                      0.96.20.2-1

gnome-software recommends no packages.

Versions of packages gnome-software suggests:
pn  fwupd                          <none>
ii  gnome-software-plugin-flatpak  3.22.5-1
pn  gnome-software-plugin-limba    <none>

-- debconf-show failed