UnsupportedOperationException from BaseLeftTuple.getBlocker

I am occasionally running into the follow exception after upgrading from 5.4.0-Final to 5.5.0-Final:

Caused by: java.lang.UnsupportedOperationException
at org.drools.reteoo.BaseLeftTuple.getBlocker(BaseLeftTuple.java:556)
at org.drools.reteoo.NotNode.modifyLeftTuple(NotNode.java:234)
at org.drools.reteoo.LeftTupleSource.doModifyLeftTuple(LeftTupleSource.java:304)
at org.drools.reteoo.LeftTupleSource.modifyLeftTuple(LeftTupleSource.java:278)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateModifyLeftTuple(SingleLeftTupleSinkAdapter.java:205)
at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateModifyObject(SingleLeftTupleSinkAdapter.java:235)
at org.drools.reteoo.LeftInputAdapterNode.modifyObject(LeftInputAdapterNode.java:170)
at org.drools.reteoo.SingleObjectSinkAdapter.propagateModifyObject(SingleObjectSinkAdapter.java:68)
at org.drools.reteoo.AlphaNode.modifyObject(AlphaNode.java:157)
at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:507)
at org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:432)
at org.drools.reteoo.ObjectTypeNode.modifyObject(ObjectTypeNode.java:314)
at org.drools.reteoo.EntryPointNode.modifyObject(EntryPointNode.java:265)
at org.drools.common.NamedEntryPoint.update(NamedEntryPoint.java:483)
at org.drools.common.NamedEntryPoint.update(NamedEntryPoint.java:383)
at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:337)

Please let me know what else I can provide to help debug. I can provide a small project to reproduce if needed.