PagePermissionsAcceptanceTest fails intermittently with DuplicateEntityException

The builds fail with error messages like the following:

java.lang.RuntimeException: org.apache.xmlrpc.XmlRpcException: java.lang.Exception: com.atlassian.core.exception.InfrastructureException: com.atlassian.user.impl.DuplicateEntityException: User [bart] already exists in Hibernate Repository
at com.atlassian.confluence.usermanagement.DefaultUserManagementHelper.xmlRpcExecute(DefaultUserManagementHelper.java:85)
at com.atlassian.confluence.usermanagement.DefaultUserManagementHelper.createUser(DefaultUserManagementHelper.java:30)
at com.atlassian.confluence.AbstractConfluenceAcceptanceTest.createUserViaHelper(AbstractConfluenceAcceptanceTest.java:1757)
at com.atlassian.confluence.PagePermissionsAcceptanceTest.setUp(PagePermissionsAcceptanceTest.java:76)
at junit.framework.TestCase.runBare(TestCase.java:125)
at net.sourceforge.jwebunit.junit.WebTestCase.runBare(WebTestCase.java:58)
at com.atlassian.confluence.PagePermissionsAcceptanceTest.runBare(PagePermissionsAcceptanceTest.java:51)
at junit.framework.TestResult$1.protect(TestResult.java:106)
at junit.framework.TestResult.runProtected(TestResult.java:124)
at junit.framework.TestResult.run(TestResult.java:109)
at junit.framework.TestCase.run(TestCase.java:118)
at junit.framework.TestSuite.runTest(TestSuite.java:208)
at junit.framework.TestSuite.run(TestSuite.java:203)
at sun.reflect.GeneratedMethodAccessor99.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.maven.surefire.junit.JUnitTestSet.execute(JUnitTestSet.java:213)
at org.apache.maven.surefire.suite.AbstractDirectoryTestSuite.executeTestSet(AbstractDirectoryTestSuite.java:140)
at org.apache.maven.surefire.suite.AbstractDirectoryTestSuite.execute(AbstractDirectoryTestSuite.java:127)
at org.apache.maven.surefire.Surefire.run(Surefire.java:177)
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:585)
at org.apache.maven.surefire.booter.SurefireBooter.runSuitesInProcess(SurefireBooter.java:345)
at org.apache.maven.surefire.booter.SurefireBooter.main(SurefireBooter.java:1009)
Caused by: org.apache.xmlrpc.XmlRpcException: java.lang.Exception: com.atlassian.core.exception.InfrastructureException: com.atlassian.user.impl.DuplicateEntityException: User [bart] already exists in Hibernate Repository
at org.apache.xmlrpc.XmlRpcClientResponseProcessor.decodeException(XmlRpcClientResponseProcessor.java:102)
at org.apache.xmlrpc.XmlRpcClientResponseProcessor.decodeResponse(XmlRpcClientResponseProcessor.java:69)
at org.apache.xmlrpc.XmlRpcClientWorker.execute(XmlRpcClientWorker.java:72)
at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:193)
at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:184)
at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:177)
at com.atlassian.confluence.AbstractConfluenceAcceptanceTest$1.execute(AbstractConfluenceAcceptanceTest.java:266)
at com.atlassian.confluence.usermanagement.DefaultUserManagementHelper.xmlRpcExecute(DefaultUserManagementHelper.java:81)
... 25 more
Caused by: org.apache.xmlrpc.XmlRpcException: java.lang.Exception: com.atlassian.core.exception.InfrastructureException: com.atlassian.user.impl.DuplicateEntityException: User [bart] already exists in Hibernate Repository
at org.apache.xmlrpc.XmlRpcClientResponseProcessor.decodeException(XmlRpcClientResponseProcessor.java:102)
at org.apache.xmlrpc.XmlRpcClientResponseProcessor.decodeResponse(XmlRpcClientResponseProcessor.java:69)
at org.apache.xmlrpc.XmlRpcClientWorker.execute(XmlRpcClientWorker.java:72)
at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:193)
at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:184)
at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:177)
at com.atlassian.confluence.AbstractConfluenceAcceptanceTest$1.execute(AbstractConfluenceAcceptanceTest.java:266)
at com.atlassian.confluence.usermanagement.DefaultUserManagementHelper.xmlRpcExecute(DefaultUserManagementHelper.java:81)
... 25 more