unity actively overrides system-wide gsettings as current user, making some vendor overrides ineffective

How to reproduce:
as root execute
# echo -e "[org.gnome.desktop.input-sources]\nsources=[('xkb', 'us'), ('xkb', 'hu')]\n\n" >> /usr/share/glib-2.0/schemas/99_my.gschema.override
# echo -e "[org.compiz.unityshell]\nlauncher-minimize-window=true\n\n" >> /usr/share/glib-2.0/schemas/99_my.gschema.override
# glib-compile-schemas /usr/share/glib-2.0/schemas
and, either remove contents of home directory or create a new user,
and, reboot and log in as the appropriate user.

Result is that launcher-minimize-window settings=true as expected and launcher behaves accordingly, however input sources is just [('xkb', 'us')], where as it should be [('xkb', 'us'), ('xkb', 'hu')].

The launcher-minimize-window is just a random example. For most settings the vendor override method works.

But for a few, like "org.gnome.desktop.input-sources sources", they will not take effect, as some process, related to Unity, will override them for the current user after login.

Proof of this, is that running `gsettings reset org.gnome.desktop.input-sources sources` will result in [('xkb', 'us'), ('xkb', 'hu')], and the panel offering both layouts. Hence the vendor-override-method of setting system-wide defaults does work, but Unity ruins it for a few settings.

The proof that this bug is in Unity is that, installing another desktop environment, like gnome-shell, and logging into it, leaves all the system-wide defaults effective.

This bug makes vendor overrides, that should affect all "fresh" user accounts, ineffective.

The appropriate behaviour would be that a new user, or one that has its home directory cleared, to have the system-wide default gsettings in effect for their unity session.

Original problem statement: http://askubuntu.com/questions/582083/what-is-overriding-the-systemwide-keyboard-layout-settings

To get a more comprehensive but still incomplete listing of the settings that Unity overrides, log in into a "fresh" Unity session,
$ gsettings list-recursively >/tmp/01
$ gsettings list-schemas | xargs -n 1 gsettings reset-recursively
$ gsettings list-recursively >/tmp/02
$ diff /tmp/0* | less
This listing is incomplete, because it only lists non-relocatable schemas, and also because your system-wide defaults may match those of what Unity sets the users settings to. For example, not changing the layout setting to "[('xkb', 'us'), ('xkb', 'hu')]" with a vendor override, would cause it not to be listed.