ConcurrentModificationException in CompositeClassLoader$CachingLoader in multithreading environment

Sometimes we get this exception when executing rules from multiple threads at first time after application server starts, probably same rule file.

Here is our environment:
1. We are using precompiled knowledge base by serialized into file and deserialize it from file when using it;
2. Use same knowledge base object for all threads;
3. Call newStatelessKnowledgeSession from same knowledge base for every thread when executing rules;
4. stateless session is never cached or shared among threads;

Following are stack trace:

[java.util.ConcurrentModificationException] concurrent access to HashMap attempted by Thread[ORB.thread.pool :

3,5,main]
at java.util.HashMap.onExit(HashMap.java:226)
at java.util.HashMap.transfer(HashMap.java:690)
at java.util.HashMap.resize(HashMap.java:676)
at java.util.HashMap.addEntry(HashMap.java:1049)
at java.util.HashMap.put(HashMap.java:561)
at org.drools.util.CompositeClassLoader$CachingLoader.load(CompositeClassLoader.java:271)
at org.drools.util.CompositeClassLoader$CachingLoader.load(CompositeClassLoader.java:237)
at org.drools.util.CompositeClassLoader.loadClass(CompositeClassLoader.java:88)
at java.lang.ClassLoader.loadClass(ClassLoader.java:597)
at java.lang.Class.forNameImpl(Native Method)
at java.lang.Class.forName(Class.java:163)
at org.mvel2.ParserConfiguration.checkForDynamicImport(ParserConfiguration.java:159)
at org.mvel2.ParserConfiguration.hasImport(ParserConfiguration.java:187)
at org.mvel2.ParserContext.hasImport(ParserContext.java:352)
at org.mvel2.compiler.PropertyVerifier.getBeanProperty(PropertyVerifier.java:163)
at org.mvel2.compiler.PropertyVerifier.analyze(PropertyVerifier.java:117)
at org.mvel2.compiler.ExpressionCompiler.verify(ExpressionCompiler.java:381)
at org.mvel2.compiler.ExpressionCompiler._compile(ExpressionCompiler.java:273)
at org.mvel2.util.ParseTools.subCompileExpression(ParseTools.java:2137)
at org.mvel2.ast.Substatement.<init>(Substatement.java:38)
at org.mvel2.compiler.AbstractParser.nextToken(AbstractParser.java:1073)
at org.mvel2.compiler.ExpressionCompiler._compile(ExpressionCompiler.java:128)
at org.mvel2.util.ParseTools.subCompileExpression(ParseTools.java:2137)
at org.mvel2.ast.Negation.<init>(Negation.java:40)
at org.mvel2.compiler.AbstractParser.nextToken(AbstractParser.java:1181)
at org.mvel2.compiler.ExpressionCompiler._compile(ExpressionCompiler.java:128)
at org.mvel2.compiler.ExpressionCompiler.compile(ExpressionCompiler.java:62)
at org.mvel2.MVEL.compileExpression(MVEL.java:810)
at org.drools.base.mvel.MVELCompilationUnit.compile(MVELCompilationUnit.java:442)
at org.drools.base.mvel.MVELCompilationUnit.getCompiledExpression(MVELCompilationUnit.java:238)
at org.drools.rule.constraint.MvelConstraint.createMvelConditionEvaluator(MvelConstraint.java:173)
at org.drools.rule.constraint.MvelConstraint.evaluate(MvelConstraint.java:157)
at org.drools.rule.constraint.MvelConstraint.isAllowed(MvelConstraint.java:124)
at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:137)
at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:497)
at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:382)
at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235)
at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:337)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:298)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:888)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847)
at org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:269)
at org.drools.impl.StatelessKnowledgeSessionImpl.execute(StatelessKnowledgeSessionImpl.java:303)
at com.validators.Validator.execute(Validator.java:436)
at com.ejb.EJBBean.validate(EJBBean.java:122)
at com.ejb._EJSRemote0SLEJBBean_3a6166f4_Tie.validate(_EJSRemote0SLEJBBean_3a6166f4_Tie.java)
at com.ibm.CORBA.iiop.ServerDelegate.dispatchInvokeHandler(ServerDelegate.java:621)
at com.ibm.CORBA.iiop.ServerDelegate.dispatch(ServerDelegate.java:474)
at com.ibm.rmi.iiop.ORB.process(ORB.java:503)
at com.ibm.CORBA.iiop.ORB.process(ORB.java:1571)
at com.ibm.rmi.iiop.Connection.respondTo(Connection.java:2703)
at com.ibm.rmi.iiop.Connection.doWork(Connection.java:2577)
at com.ibm.rmi.iiop.WorkUnitImpl.doWork(WorkUnitImpl.java:62)
at com.ibm.ejs.oa.pool.PooledThread.run(ThreadPool.java:118)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1551)