Access denied ("java.lang.RuntimePermission" "modifyThread") highly intermittent, but e.g. in store.RecoveryAfterBackup test

I got a report of the following intermittent (6/60) exception in store.RecoveryAfterBackupTest.
Exception in thread "main" java.security.AccessControlException: Access denied ("java.lang.RuntimePermission" "modifyThread")
at java.security.AccessController.throwACE(AccessController.java:100)
at java.security.AccessController.checkPermission(AccessController.java:174)
at java.lang.SecurityManager.checkPermission(SecurityManager.java:549)
at java.lang.SecurityManager.checkAccess(SecurityManager.java:676)
at java.lang.Thread.checkAccess(Thread.java:459)
at java.lang.Thread.interrupt(Thread.java:588)
at org.apache.derby.iapi.services.context.ContextService$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(AccessController.java:274)
at org.apache.derby.iapi.services.context.ContextService.notifyAllActiveThreads(Unknown Source)
at org.apache.derby.impl.services.monitor.BaseMonitor.shutdown(Unknown Source)
at org.apache.derby.jdbc.InternalDriver.connect(Unknown Source)
at org.apache.derby.jdbc.Driver20.connect(Unknown Source)
at org.apache.derby.jdbc.AutoloadedDriver.connect(Unknown Source)
at java.sql.DriverManager.getConnection(DriverManager.java:571)
at java.sql.DriverManager.getConnection(DriverManager.java:233)
at org.apache.derbyTesting.functionTests.util.TestUtil.getConnection(TestUtil.java:836)
at org.apache.derbyTesting.functionTests.tests.store.RecoveryAfterBackup.main(RecoveryAfterBackup.java:82)

modifyThread is a necessary permission if interrupting a thread other than the current thread but is not in our policy file for derby.jar.

The relevant code in ContextService is:
for (ContextManager cm : allContexts) {

Thread active = cm.activeThread;

if (active == me)
continue;

if (active == null)
continue;

final Thread fActive = active;
if (cm.setInterrupted(c))
{
AccessController.doPrivileged(
new PrivilegedAction<Void>() {
public Void run()

{ fActive.interrupt(); return null; }

});
}

I am not sure why this has never come up before. Are we expecting in this context that fActive is the current thread?