Here's the smoking gun...
The gateway is timing out after 1 second and your reply is taking 2.6 seconds.
2011-05-10 13:37:37,108 [socketExecutor-2] | DEBUG | postSend
2011-05-10 13:37:38,123 [socketExecutor-2] | DEBUG | null reply received
2011-05-10 13:37:39,776 [asmTxExecutor-3] | DEBUG | handler 'org.springframework.integration.handler.BridgeHandler@57ee57ee' sending reply Message:
The default timeout for a gateway is 1 second; this can be increased by using the reply-timeout attribute on the inbound gateway.
As you have seen, this won't happen on a single thread, obviously, because the thread is doing work rather than waiting for a response.
Hope that helps.