I have managed to reduce down the project from mxv into a single unit test that can be added to Misc2Test. I turned tracing on, and it fails while evaluating R1: 2014-02-25 05:00:16,192 [main] TRACE Rule[name=R1] segments=2 TupleSets[insertSize=0, deleteSize=0, updateSize=0] 2014-02-25 05:00:16,192 [main] TRACE 11 [JoinNode(5) - [ClassObjectType class=org.drools.compiler.integrationtests.Misc2Test$Foo2]] TupleSets[insertSize=0, deleteSize=0, updateSize=0] 2014-02-25 05:00:16,192 [main] TRACE Skip Segment 0 2014-02-25 05:00:16,192 [main] TRACE Segment 1 2014-02-25 05:00:16,192 [main] TRACE 11 [JoinNode(7) - [ClassObjectType class=org.drools.compiler.Person]] TupleSets[insertSize=0, deleteSize=0, updateSize=1] 2014-02-25 05:00:16,193 [main] TRACE rightTuples TupleSets[insertSize=1, deleteSize=0, updateSize=0] I've provided the new test and the full trace log below. The problem is the node sharing of Foo2. R1 thinks it's propagating an update, when it never passed R1's Foo2 before, so it should propagate as an update for R2 but an insert for R1. I suspect the problem is related to the SegmentPropagator when it is updated after moving from the first shared segment, to the two child segments. Please try to avoid submitting project jars. It takes a lot more time for us to setup and work with, which will delay our time in getting back to you. Ideally create a reduced single test method, as per blow, that is self contained, and submit it with pull request and associated JIRA. see: http://docs.jboss.org/drools/release/5.6.0.Final/droolsjbpm-introduction-... @Test*public void *testSharedNotWithLeftUpdateAndRightInsert() *throws *Exception { String str = *"import " *+ Foo.*class*.getCanonicalName() + *";**\n**" *+ *"import " *+ Foo2.*class*.getCanonicalName() + *";**\n**" *+ *"import " *+ Person.*class*.getCanonicalName() + *";**\n**" *+ *"rule R1 when**\n**" *+ *" f1 : Foo( )**\n**" *+ *" Foo2( )**\n**" *+ *" Person( age == f1.x )**\n**" *+ *"then**\n**" *+ *"end**\n**" *+ *"rule R2 when**\n**" *+ *" Foo( )**\n**" *+ *" f2 : Foo2( )**\n**" *+ *" not Person()**\n**" *+ *"then**\n**" *+ *" modify( f2 ) { x = 3};**\n**" *+ *" insert( new Person() );**\n**" *+ *"end**\n**"*; KnowledgeBase kbase = loadKnowledgeBaseFromString(str); StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession(); Foo f1 = *new *Foo(); Foo2 f2 = *new *Foo2(); ksession.insert( f1 ); ksession.insert( f2 ); *assertEquals*(2, ksession.fireAllRules() ); *assertEquals*( 3, f2.getX() );} For those interested, here is the full trace output once trace is turned on: 2014-02-25 05:13:33,610 [main] DEBUG Starting Engine in PHREAK mode 2014-02-25 05:13:33,715 [main] TRACE Adding Rule R1 2014-02-25 05:13:33,720 [main] TRACE Adding Rule R2 2014-02-25 05:13:33,809 [main] TRACE Insert [fact 0:1:1668059028:1668059028:1:DEFAULT:NON_TRAIT:org.drools.compiler.integrationtests.Misc2Test$Foo@636c8f94 ] 2014-02-25 05:13:33,822 [main] TRACE LinkNode notify=false nmask=1 smask=1 spos=0 rules= 2014-02-25 05:13:33,823 [main] TRACE LinkSegment smask=2 rmask=2 name=R2 2014-02-25 05:13:33,831 [main] TRACE LinkNode notify=true nmask=1 smask=1 spos=0 rules=[RuleMem R1], [RuleMem R2] 2014-02-25 05:13:33,832 [main] TRACE Insert [fact 0:2:588638666:588638666:2:DEFAULT:NON_TRAIT:org.drools.compiler.integrationtests.Misc2Test$Foo2@2315e9ca ] 2014-02-25 05:13:33,833 [main] TRACE BetaNode insert=1 stagedInsertWasEmpty=true 2014-02-25 05:13:33,833 [main] TRACE LinkNode notify=true nmask=2 smask=3 spos=0 rules=[RuleMem R1], [RuleMem R2] 2014-02-25 05:13:33,833 [main] TRACE LinkSegment smask=1 rmask=1 name=R1 2014-02-25 05:13:33,834 [main] TRACE LinkSegment smask=1 rmask=3 name=R2 2014-02-25 05:13:33,834 [main] TRACE LinkRule name=R2 2014-02-25 05:13:33,855 [main] TRACE Queue RuleAgendaItem [Activation rule=R2, act#=0, salience=0, tuple=null] 2014-02-25 05:13:33,856 [main] TRACE Queue Added 1 [Activation rule=R2, act#=0, salience=0, tuple=null] 2014-02-25 05:13:33,856 [main] TRACE Rule[name=R2] segments=2 TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,856 [main] TRACE 1 [JoinNode(5) - [ClassObjectType class=org.drools.compiler.integrationtests.Misc2Test$Foo2]] TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,857 [main] TRACE Segment 0 2014-02-25 05:13:33,857 [main] TRACE 1 [JoinNode(5) - [ClassObjectType class=org.drools.compiler.integrationtests.Misc2Test$Foo2]] TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,865 [main] TRACE rightTuples TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,867 [main] TRACE Segment 1 2014-02-25 05:13:33,867 [main] TRACE 2 [NotNode(9) - [ClassObjectType class=org.drools.compiler.Person]] TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,867 [main] TRACE Segment 1 2014-02-25 05:13:33,868 [main] TRACE 2 [NotNode(9) - [ClassObjectType class=org.drools.compiler.Person]] TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,868 [main] TRACE rightTuples TupleSets[insertSize=0, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,870 [main] TRACE 3 [RuleTerminalNode(10): rule=R2] TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,871 [main] TRACE Segment 1 2014-02-25 05:13:33,871 [main] TRACE 3 [RuleTerminalNode(10): rule=R2] TupleSets[insertSize=1, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,871 [main] TRACE Fire "R2" [[ R2 active=false ] [ null [fact 0:2:588638666:588638666:2:DEFAULT:NON_TRAIT:org.drools.compiler.integrationtests.Misc2Test$Foo2@2315e9ca ] [fact 0:1:1668059028:1668059028:1:DEFAULT:NON_TRAIT:org.drools.compiler.integrationtests.Misc2Test$Foo@636c8f94] ] ] 2014-02-25 05:13:33,877 [main] TRACE Update [fact 0:2:588638666:588638666:3:DEFAULT:NON_TRAIT:org.drools.compiler.integrationtests.Misc2Test$Foo2@2315e9ca ] 2014-02-25 05:13:33,879 [main] TRACE LinkSegment smask=1 rmask=1 name=R1 2014-02-25 05:13:33,879 [main] TRACE LinkSegment smask=1 rmask=3 name=R2 2014-02-25 05:13:33,879 [main] TRACE LinkRule name=R2 2014-02-25 05:13:33,880 [main] TRACE Insert [fact 0:3:1618732380:-62068830:4:DEFAULT:LEGACY_TRAITABLE:[Person name='null age='0' likes='null']] 2014-02-25 05:13:33,880 [main] TRACE BetaNode insert=1 stagedInsertWasEmpty=true 2014-02-25 05:13:33,880 [main] TRACE LinkNode notify=true nmask=1 smask=1 spos=1 rules=[RuleMem R1] 2014-02-25 05:13:33,880 [main] TRACE LinkSegment smask=2 rmask=3 name=R1 2014-02-25 05:13:33,881 [main] TRACE LinkRule name=R1 2014-02-25 05:13:33,881 [main] TRACE Queue RuleAgendaItem [Activation rule=R1, act#=2, salience=0, tuple=null] 2014-02-25 05:13:33,881 [main] TRACE Queue Added 1 [Activation rule=R1, act#=2, salience=0, tuple=null] 2014-02-25 05:13:33,881 [main] TRACE LinkNode notify=true nmask=1 smask=1 spos=1 rules=[RuleMem R2] 2014-02-25 05:13:33,882 [main] TRACE LinkSegment smask=2 rmask=3 name=R2 2014-02-25 05:13:33,882 [main] TRACE LinkRule name=R2 2014-02-25 05:13:33,882 [main] TRACE Rule[name=R1] segments=2 TupleSets[insertSize=0, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,882 [main] TRACE 4 [JoinNode(5) - [ClassObjectType class=org.drools.compiler.integrationtests.Misc2Test$Foo2]] TupleSets[insertSize=0, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,883 [main] TRACE Segment 0 2014-02-25 05:13:33,883 [main] TRACE 4 [JoinNode(5) - [ClassObjectType class=org.drools.compiler.integrationtests.Misc2Test$Foo2]] TupleSets[insertSize=0, deleteSize=0, updateSize=0] 2014-02-25 05:13:33,884 [main] TRACE rightTuples TupleSets[insertSize=0, deleteSize=0, updateSize=1] 2014-02-25 05:13:33,884 [main] TRACE Segment 1 2014-02-25 05:13:33,884 [main] TRACE 5 [JoinNode(7) - [ClassObjectType class=org.drools.compiler.Person]] TupleSets[insertSize=0, deleteSize=0, updateSize=1] 2014-02-25 05:13:33,884 [main] TRACE Segment 1 2014-02-25 05:13:33,885 [main] TRACE 5 [JoinNode(7) - [ClassObjectType class=org.drools.compiler.Person]] TupleSets[insertSize=0, deleteSize=0, updateSize=1] 2014-02-25 05:13:33,885 [main] TRACE rightTuples TupleSets[insertSize=1, deleteSize=0, updateSize=0] java.lang.NullPointerException at org.drools.core.util.index.LeftTupleIndexHashTable.remove(LeftTupleIndexHashTable.java:386) at org.drools.core.phreak.RuleNetworkEvaluator.doUpdatesReorderLeftMemory(RuleNetworkEvaluator.java:799)