public static class Firings {
        private final List<String> list = new ArrayList<>();
        public List<String> getList() {
            return list;
        }
    }
    @Test
    public void testPeerUpdate() {
        // DROOLS-6783
        final String str =
                "import " + Firings.class.getCanonicalName() + "\n" +
                "\n" +
                "rule R1 when\n" +
                "  Integer()\n" +
                "  $f : Firings( list not contains \"R1\" )\n" +
                "then\n" +
                "  $f.getList().add(\"R1\");\n" +
                "  update($f);\n" +
                "end\n" +
                "\n" +
                "rule R2 agenda-group \"x\" when\n" +
                "  Integer()\n" +
                "  Firings( $l : list )\n" +
                "  String()\n" +
                "then\n" +
                "end\n" +
                "\n" +
                "rule R3 agenda-group \"x\" when\n" +
                "  Integer()\n" +
                "  Firings( $l : list )\n" +
                "then\n" +
                "end\n" +
                "\n" +
                "rule R4 when\n" +
                "  Integer()\n" +
                "  Firings( $l : list )\n" +
                "then\n" +
                "end\n" +
                "\n" +
                "rule R5 when\n" +
                "  Integer()\n" +
                "  $f : Firings( list not contains \"R5\" )\n" +
                "then\n" +
                "  $f.getList().add(\"R5\");\n" +
                "  update($f);\n" +
                "end";
        KieBase kbase = KieBaseUtil.getKieBaseFromKieModuleFromDrl("test", kieBaseTestConfiguration, str);
        KieSession ksession = kbase.newKieSession();
        ksession.insert(1);
        ksession.insert(new Firings());
        ksession.getAgenda().getAgendaGroup("x").setFocus();
        assertEquals( 5, ksession.fireAllRules() );
    }

java.lang.IllegalStateException: It should not be possible that an existing udpate is staged, when an insert is later requested.
    at org.drools.core.phreak.SegmentPropagator.updateChildLeftTupleDuringInsert(SegmentPropagator.java:152)
    at org.drools.core.phreak.SegmentPropagator.processPeerInserts(SegmentPropagator.java:95)
    at org.drools.core.phreak.SegmentPropagator.processPeers(SegmentPropagator.java:69)
    at org.drools.core.phreak.SegmentPropagator.propagate(SegmentPropagator.java:45)
    at org.drools.core.phreak.RuleNetworkEvaluator.innerEval(RuleNetworkEvaluator.java:359)
    at org.drools.core.phreak.RuleNetworkEvaluator.outerEval(RuleNetworkEvaluator.java:181)
    at org.drools.core.phreak.RuleNetworkEvaluator.evaluateNetwork(RuleNetworkEvaluator.java:139)
    at org.drools.core.phreak.RuleExecutor.reEvaluateNetwork(RuleExecutor.java:234)
    at org.drools.core.phreak.RuleExecutor.evaluateNetworkAndFire(RuleExecutor.java:90)
    at org.drools.core.concurrent.AbstractRuleEvaluator.internalEvaluateAndFire(AbstractRuleEvaluator.java:33)
    at org.drools.core.concurrent.SequentialRuleEvaluator.evaluateAndFire(SequentialRuleEvaluator.java:43)
    at org.drools.kiesession.agenda.DefaultAgenda.fireLoop(DefaultAgenda.java:754)
    at org.drools.kiesession.agenda.DefaultAgenda.internalFireAllRules(DefaultAgenda.java:701)
    at org.drools.kiesession.agenda.DefaultAgenda.fireAllRules(DefaultAgenda.java:693)
    at org.drools.kiesession.session.StatefulKnowledgeSessionImpl.internalFireAllRules(StatefulKnowledgeSessionImpl.java:1092)
    at org.drools.kiesession.session.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1083)
    at org.drools.kiesession.session.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:1067)
    at org.drools.mvel.integrationtests.session.UpdateTest.testPeerUpdate(UpdateTest.java:633)