Error "Unexpected exception executing action org.drools.reteoo.PropagationQueuingNode$PropagateAction@631b86c7" with two after-clauses

I'm getting the following Error "Unexpected exception executing action org.drools.reteoo.PropagationQueuingNode$PropagateAction@631b86c7" with one off my rules in my project.
The problem is linked with the use of two after statements in one rule.
If I delete one of them everything works like a charm.
The rule looks like this:

// Regeln
rule "Vergessene Herdplatte"

when
// Platte wurde eingeschaltet und es steht kein Topf auf ihr
$platte: HerdplatteEingeschaltet( plateOccupied == false ) from entry-point events
// und in den nächsten 20 sek wird die gleiche Platte nicht ausgeschaltet
not( HerdplatteAusgeschaltet( this.nummer == $platte.nummer, this after[0s,20s] $platte ) from entry-point events )
// oder es wird in den nächsten 20 sek kein Topf auf die Platte gestellt
not( TopfAufHerdplatte( this.nummer == $platte.nummer, this after[0s,20s] $platte ) from entry-point events )
then
System.out.println("Vergessene Herdplatte erkannt!");

end

If I comment one of the not-clause out, it works.
I created an unit-test which reproduces the exception.
And here the Failure Trace:

org.drools.RuntimeDroolsException: Unexpected exception executing action org.drools.reteoo.PropagationQueuingNode$PropagateAction@631b86c7
at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1473)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:182)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:145)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:96)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:44)
at com.sample.FusionTest.testRule(FusionTest.java:79)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: java.lang.NullPointerException
at org.drools.time.impl.CompositeMaxDurationTimer.createTrigger(CompositeMaxDurationTimer.java:58)
at org.drools.common.Scheduler.scheduleAgendaItem(Scheduler.java:55)
at org.drools.common.DefaultAgenda.scheduleItem(DefaultAgenda.java:314)
at org.drools.reteoo.RuleTerminalNode.assertLeftTuple(RuleTerminalNode.java:185)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:189)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:78)
at org.drools.reteoo.NotNode.assertLeftTuple(NotNode.java:101)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:189)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:78)
at org.drools.reteoo.NotNode.assertLeftTuple(NotNode.java:101)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:189)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:64)
at org.drools.reteoo.JoinNode.assertObject(JoinNode.java:128)
at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:59)
at org.drools.reteoo.PropagationQueuingNode$AssertAction.execute(PropagationQueuingNode.java:347)
at org.drools.reteoo.PropagationQueuingNode.propagateActions(PropagationQueuingNode.java:229)
at org.drools.reteoo.PropagationQueuingNode$PropagateAction.execute(PropagationQueuingNode.java:443)
at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1471)
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