Bug#753919: gnome-control-center: unlock button does nothing

[Traumschule]

Same with a fresh debian 9.6:

Clicking 'Unlock' does nothing, console shows:

(gnome-control-center:11030): Gtk-WARNING **: Error acquiring
permission: Failed to acquire permission for action-id
org.gnome.controlcenter.datetime.configure

ii  policykit-1		0.105-18+deb9u1	i386
ii policykit-1-gnome	0.105-6		i386

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