Comment 15 for bug 1732185

check-new-release-gtk in ubuntu-release-upgrader has this code that must also be fixed:

123 def on_button_upgrade_now_clicked(self, button):
124 logging.debug("upgrade now")
125 extra_args = ""
126 if options.devel_release:
127 extra_args = extra_args + " --devel-release"
128 if options.proposed_release:
129 extra_args = extra_args + " --proposed"
130 os.execl("/bin/sh", "/bin/sh", "-c",
131 "/usr/bin/pkexec /usr/bin/do-release-upgrade "
132 "--frontend=DistUpgradeViewGtk3%s" % extra_args)