On upgrade of HSQLDB from 1.8.0.2 to 1.8.0.7 the following testcase seems to consistently fail:
org.jboss.test.cmp2.idxandusersql.test.IdxAndUsersqlUnitTestCase::testCMRmn2
Error: FKey cmr2_id is indexed

The test reports say:
junit.framework.AssertionFailedError: Error: FKey cmr2_id is indexed
at org.jboss.test.cmp2.idxandusersql.test.IdxAndUsersqlUnitTestCase.testCMRmn2(IdxAndUsersqlUnitTestCase.java:190)
at net.sourceforge.junitejb.EJBTestCase.runBare(EJBTestCase.java:133)
at net.sourceforge.junitejb.EJBTestRunnerBean.runTestCase(EJBTestRunnerBean.java:102)
at net.sourceforge.junitejb.EJBTestRunnerBean.run(EJBTestRunnerBean.java:44)
at org.jboss.invocation.Invocation.performCall(Invocation.java:359)
at org.jboss.ejb.StatelessSessionContainer$ContainerInterceptor.invoke(StatelessSessionContainer.java:237)
at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:158)
at org.jboss.ejb.plugins.CallValidationInterceptor.invoke(CallValidationInterceptor.java:63)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:121)
at org.jboss.ejb.plugins.AbstractTxInterceptorBMT.invokeNext(AbstractTxInterceptorBMT.java:173)
at org.jboss.ejb.plugins.TxInterceptorBMT.invoke(TxInterceptorBMT.java:77)
at org.jboss.ejb.plugins.StatelessSessionInstanceInterceptor.invoke(StatelessSessionInstanceInterceptor.java:169)
at org.jboss.ejb.plugins.SecurityInterceptor.invoke(SecurityInterceptor.java:168)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:205)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:136)
at org.jboss.ejb.SessionContainer.internalInvoke(SessionContainer.java:648)

The sourcefile for the test says:
/*

• Look for indices on the m:n mapping table
• This is for hsql a strange case, at indices are put there
• anyway, but it has been told that other databases don't do
• it by themselves, so we check if the creation succeeds.
  */
  Would like to get an experts opinion on it