Incremental compilation is not correctly synchronized and then a kiesession can fire when the underlying rule base is in an inconsistent state. The test case below shows the problem

    @Test(timeout = 10000)
    public void testIncrementalCompilationSynchronization() throws Exception {
        final KieServices kieServices = KieServices.Factory.get();

        ReleaseId releaseId = kieServices.newReleaseId("org.kie.test", "sync-scanner-test", "1.0.0");
        createAndDeployJar( kieServices, releaseId, createDRL("rule0") );

        final KieContainer kieContainer = kieServices.newKieContainer(releaseId);

        KieSession kieSession = kieContainer.newKieSession();
        List<String> list = new ArrayList<String>();
        kieSession.setGlobal("list", list);
        kieSession.fireAllRules();
        kieSession.dispose();
        assertEquals(1, list.size());

        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i < 10; i++) {
                    ReleaseId releaseId = kieServices.newReleaseId("org.kie.test", "sync-scanner-test", "1.0." + i);
                    createAndDeployJar( kieServices, releaseId, createDRL("rule" + i) );
                    kieContainer.updateToVersion(releaseId);
                }
            }
        });

        t.setDaemon(true);
        t.start();

        while (true) {
            kieSession = kieContainer.newKieSession();
            list = new ArrayList<String>();
            kieSession.setGlobal("list", list);
            kieSession.fireAllRules();
            kieSession.dispose();
            assertEquals(1, list.size());
            if (list.get(0).equals("rule9")) {
                break;
            }
        }
    }

    private String createDRL(String ruleName) {
        return "package org.kie.test\n" +
               "global java.util.List list\n" +
               "rule " + ruleName + "\n" +
               "when\n" +
               "then\n" +
               "list.add( drools.getRule().getName() );\n" +
               "end\n";
    }