Repeated NullPointerExceptions on Shutdown; shutdown fails to complete

When I go to shutdown Bamboo, I get errors like this:

8/03/2007 12:52:45 net.sf.hibernate.util.JDBCExceptionReporter logExceptions
WARNING: SQL Error: 0, SQLState: null
8/03/2007 12:52:45 net.sf.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: com.mchange.v2.c3p0.PoolBackedDataSource@252187a8 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@da0c3322 [ acquireIncrement -> 1, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> z8kflt7ld47pvkmymji0|1bdbfec, idleConnectionTestPeriod -> 100, initialPoolSize -> 0, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 30, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 0, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@7cb2cc23 [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> z8kflt7ld47pvkmymji0|ecd92c, jdbcUrl -> jdbc:hsqldb:/home/robertdw/bamboo-home/database/defaultdb, properties ->

], preferredTestQuery -> null, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> z8kflt7ld47pvkmymji0|16dba0a, numHelperThreads -> 3 ] has been closed() – you can no longer use it.
java.lang.NullPointerException
at org.springframework.orm.hibernate.SessionFactoryUtils.closeSessionOrRegisterDeferredClose(SessionFactoryUtils.java:709)
at org.springframework.orm.hibernate.SessionFactoryUtils.releaseSession(SessionFactoryUtils.java:696)
at org.springframework.orm.hibernate.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:453)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:283)
at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:226)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:89)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:170)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:176)
at $Proxy10.getAllBuilds(Unknown Source)
at com.atlassian.bamboo.container.ShutdownHook.run(ShutdownHook.java:28)

These errors repeat once every second, and prevent the Tomcat instance from actually stopping - it is necessary to kill the process manually before restarting.