Hibernate ConnectionManager.openConnection() sometimes hangs when using ON_CLOSE release mode

Issue

My application hangs on a query after a certain number of queries have been performed.  Before each query I open the session, and close it immediately afterwards.  Below is the end of the log.  As you will see it appears to be hanging on "ConnectionManager.openConnection(444)". I have looked at the database connections and there is a normal amount (3) when it hangs so it is not as if there are excess connections hanging around.  Is there something I need to configure to get hibernate to deal with a large amount of queries?  It seems to cope up to a point.

DEBUG - StatefulPersistenceContext.initializeNonLazyCollections(860) | initializing non-lazy collections
DEBUG - ConnectionManager.afterTransaction(325) | transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!
DEBUG - ConnectionManager.closeConnection(464) | releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]
DEBUG - ConnectionManager.afterTransaction(325) | transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!
DEBUG - SessionImpl.<init>(247) | opened session at timestamp: 12749669784
DEBUG - AbstractBatcher.logOpenPreparedStatement(410) | about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
DEBUG - ConnectionManager.openConnection(444) | opening JDBC connection
DEBUG - SQLStatementLogger.logStatement(111) | select ACCT001 from ACCT where ACCT029 = 'L' and ACCT011 <> 'C' and ACCT303 = '130' and ACCT014 like '%Collection%' and ACCT514 <= ? and ACCT003 = ?
Hibernate: select ACCT001 from ACCT where ACCT029 = 'L' and ACCT011 <> 'C' and ACCT303 = '130' and ACCT014 like '%Collection%' and ACCT514 <= ? and ACCT003 = ?
DEBUG - Loader.bindNamedParameters(1768) | bindNamedParameters() java.util.GregorianCalendar[time=1274828400000,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Europe/London",offset=0,dstSavings=3600000,useDaylight=true,transitions=242,lastRule=java.util.SimpleTimeZone[id=Europe/London,offset=0,dstSavings=3600000,useDaylight=true,startYear=0,startMode=2,startMonth=2,startDay=-1,startDayOfWeek=1,startTime=3600000,startTimeMode=2,endMode=2,endMonth=9,endDay=-1,endDayOfWeek=1,endTime=3600000,endTimeMode=2]],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2010,MONTH=4,WEEK_OF_YEAR=21,WEEK_OF_MONTH=4,DAY_OF_MONTH=26,DAY_OF_YEAR=146,DAY_OF_WEEK=4,DAY_OF_WEEK_IN_MONTH=4,AM_PM=0,HOUR=0,HOUR_OF_DAY=0,MINUTE=0,SECOND=0,MILLISECOND=0,ZONE_OFFSET=0,DST_OFFSET=3600000] -> startDate [1]
DEBUG - Loader.bindNamedParameters(1768) | bindNamedParameters() WF -> portfolio [2]
DEBUG - AbstractBatcher.logOpenResults(426) | about to open ResultSet (open ResultSets: 0, globally: 0)
DEBUG - AbstractBatcher.logCloseResults(433) | about to close ResultSet (open ResultSets: 1, globally: 1)
DEBUG - AbstractBatcher.logClosePreparedStatement(418) | about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
DEBUG - StatefulPersistenceContext.initializeNonLazyCollections(860) | initializing non-lazy collections
DEBUG - ConnectionManager.afterTransaction(325) | transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!
Row: 1.006366E7
break
DEBUG - SessionImpl.<init>(247) | opened session at timestamp: 12749669784
DEBUG - AbstractBatcher.logOpenPreparedStatement(410) | about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
DEBUG - ConnectionManager.openConnection(444) | opening JDBC connection