hang in suites.all with ibm 1.5 on AIX after ttestDefaultProperties

The test run for 10.5.2.0 hung in suites.All. The console output (the run was with -Dderby.tests.trace=true) showed ttestDefaultProperties had successfully completed but the run was halted.
ps -eaf | grep java showed the process that kicked off suites.All, and a networkserver process with the following flags:

• classpath <classpath including derby.jar, derbytools.jar, derbyclient.jar, derbynet.jar, derbyTesting.jar, derbyrun.jar, derbyTesting.jar and junit.jar> -Dderby.drda.logConnections= -Dderby.drda.traceAll= -Dderby.drda.traceDirectory= -Dderby.drda.keepAlive= -Dderby.drda.timeSlice= -Dderby.drda.host= -Dderby.drda.portNumber= -derby.drda.minThreads= -Dderby.drda.maxThreads= -Dderby.drda.startNetworkServer= -Dderby.drda.debug= org.apache.derby.drda.NetworkServerControl start -h localhost -p 1527
  This process had been sitting for 2 days.
  After killing the NetworkServerControl process, the test continued successfully (except for DERBY-4186, fixed in trunk), but the following was put out to the console:
  START-SPAWNED:SpawnedNetworkServer STANDARD OUTPUT: exit code=137
  2009-07-18 03:16:07.157 GMT : Security manager installed using the Basic server
  security policy.
  2009-07-18 03:16:09.169 GMT : Apache Derby Network Server - 10.5.2.0 - (794445)
  started and ready to accept connections on port 1527
  END-SPAWNED :SpawnedNetworkServer STANDARD OUTPUT: