How to troubleshoot SSL "bad record MAC" exception

Question

I am using an Apache CXF client, running in a Windows Java 1.6.0_29-b11 VM to connect to an IBM mainframe (I believe it is zSeries), and invoking a SOAP Web Service running there. The connection is done through SSL/TLS, and most of the time works fine.

However, from time to time I have SSL Exceptions with a bad record MAC message. Here is the output of the program using with the javax.net.debug property.

2011-11-16 12:32:37,731 INFO  LoggingOutInterceptor: Outbound Message
---------------------------
ID: 29
Address: https://1.2.3.4/access/servlet/blabla.atk123
Encoding: UTF-8
Content-Type: text/xml
Headers: {Accept=[*/*], SOAPAction=["Blablaaction/ATK123.Execute"]}
Payload: <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"><soap:Body><ATK123.Execute xmlns="Blabla"><Usrid>WA</Usrid><Usrpwd>54321</Usrpwd><Ultautid>9999</Ultautid></ATK123.Execute></soap:Body></soap:Envelope>
--------------------------------------
pool-1-thread-1, setSoTimeout(30000) called
pool-1-thread-1, WRITE: TLSv1 Application Data, length = 321
pool-1-thread-1, WRITE: TLSv1 Application Data, length = 262
pool-1-thread-1, READ: TLSv1 Application Data, length = 483
pool-1-thread-1, READ: TLSv1 Application Data, length = 16148
pool-1-thread-1, READ: TLSv1 Application Data, length = 282
%% Invalidated:  [Session-1, SSL_RSA_WITH_RC4_128_SHA]
pool-1-thread-1, SEND TLSv1 ALERT:  fatal, description = bad_record_mac
pool-1-thread-1, WRITE: TLSv1 Alert, length = 22
pool-1-thread-1, called closeSocket()
pool-1-thread-1, handling exception: javax.net.ssl.SSLException: bad record MAC
2011-11-16 12:32:38,511 WARN  PhaseInterceptorChain: Interceptor for {Blabla}ATK123#{Blabla}Execute has thrown exception, unwinding now
org.apache.cxf.interceptor.Fault: bad record MAC
    at org.apache.cxf.interceptor.LoggingInInterceptor.logging(LoggingInInterceptor.java:144)
    at org.apache.cxf.interceptor.LoggingInInterceptor.handleMessage(LoggingInInterceptor.java:73)
    at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:263)
    at org.apache.cxf.endpoint.ClientImpl.onMessage(ClientImpl.java:797)
.... (more stuff)

Unfortunately, I don't have possibilities to modify or debug the endpoint at the server.

What could be causing this?

How can I isolate and fix this behavior?