The issue is settled now. Germany paid huge war reparations after WWII until the 1990s.
Apart from that, many of these explosives are malfunctioning bombs that were supposed to go off when firefighters and rescue personell are at the site. Such devices are pure malice; the defense argument can't justify them.
You can't randomly levy all sorts of minor nuisance onto somebody after they've conceded and signed a bunch of treaties largely drafted by the winning side meant to settle this. That's just a great way to self-sabotage your diplomatic reputation.