XmlRpcException during TeamCity build agent registration

I have installed the TeamCity build agent on my machine a few different ways- using Java Web Start and the manual .zip distribution. Both result in viable installations, as I have once or twice been able to connect and register properly with the TeamCity server. However, upon restarting (<install_location>/bin/agent.sh stop...<install_location>/bin/agent.sh start) I get the following error in teamcity-agent.log (with extra debugging turned on in the log4j config file).

    [2013-04-03 09:05:09,870]  DEBUG -   jetbrains.buildServer.XMLRPC - faultStringjava.lang.RuntimeException: org.jdom.input.JDOMParseException: Error on line 28: XML document structures must start and end within the same entity.faultCode0 
    [2013-04-03 09:05:09,878]  DEBUG - buildServer.AGENT.registration - jetbrains.buildServer.xmlrpc.RemoteCallException: Call http://teamcityserver:8080/RPC2 buildServer.registerAgent3: org.apache.xmlrpc.XmlRpcException: java.lang.RuntimeException: org.jdom.input.JDOMParseException: Error on line 28: XML document structures must start and end within the same entity. 
    jetbrains.buildServer.xmlrpc.RemoteCallException: Call http://teamcityserver:8080/RPC2 buildServer.registerAgent3: org.apache.xmlrpc.XmlRpcException: java.lang.RuntimeException: org.jdom.input.JDOMParseException: Error on line 28: XML document structures must start and end within the same entity.
      at jetbrains.buildServer.xmlrpc.AbstractXmlRpcTarget.call(AbstractXmlRpcTarget.java:94)
      at jetbrains.buildServer.agent.impl.ServerXmlRpcProxy.registerAgent3(ServerXmlRpcProxy.java:62)
      at jetbrains.buildServer.agent.impl.BuildAgentImpl.doRegisterOnBuildServer(BuildAgentImpl.java:776)
      at jetbrains.buildServer.agent.impl.BuildAgentImpl.registerOnBuildServer(BuildAgentImpl.java:748)
      at jetbrains.buildServer.agent.impl.ServerMonitor.run(ServerMonitor.java:71)
    Caused by: org.apache.xmlrpc.XmlRpcException: java.lang.RuntimeException: org.jdom.input.JDOMParseException: Error on line 28: XML document structures must start and end within the same entity.
      at org.apache.xmlrpc.XmlRpcClientResponseProcessor.decodeException(XmlRpcClientResponseProcessor.java:104)
      at org.apache.xmlrpc.XmlRpcClientResponseProcessor.decodeResponse(XmlRpcClientResponseProcessor.java:71)
      at org.apache.xmlrpc.XmlRpcClientWorker.execute(XmlRpcClientWorker.java:73)
      at org.apache.xmlrpc.TCXmlRpcClient$1.execute(TCXmlRpcClient.java:89)
      at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:194)
      at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:185)
      at org.apache.xmlrpc.XmlRpcClient.execute(XmlRpcClient.java:178)
      at jetbrains.buildServer.xmlrpc.impl.CommonsXmlRpcTargetImpl$1.execute(CommonsXmlRpcTargetImpl.java:72)
      at jetbrains.buildServer.xmlrpc.AbstractXmlRpcTarget.call(AbstractXmlRpcTarget.java:84)
      ... 4 more
    [2013-04-03 09:05:09,878]   WARN - buildServer.AGENT.registration - Call http://teamcityserver:8080/RPC2 buildServer.registerAgent3: org.apache.xmlrpc.XmlRpcException: java.lang.RuntimeException: org.jdom.input.JDOMParseException: Error on line 28: XML document structures must start and end within the same entity. 
    [2013-04-03 09:05:09,878]   WARN - buildServer.AGENT.registration - Connection to TeamCity server is probably lost. Will be trying to restore it. Take a look at logs/teamcity-agent.log for details (unless you're using custom logging). 

This is the xml in question according to the logs with extra xmlrpc debugging:

<?xml version="1.0"?><methodCall><methodName>buildServer.registerAgent3</methodName><params><param><value><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
<agentDetails agentName="aaronhbox_0" agentPort="9090" authToken="" osName="Linux, version 3.5.0-17-generic">
  <alternativeAddresses>
    <address>10.2.1.232</address>
    <address>192.168.225.1</address>
    <address>192.168.80.1</address>
  </alternativeAddresses>
  <availableRunners>
    <runner runType="Ant" />
    <runner runType="Duplicator" />
    <runner runType="gradle-runner" />
    <runner runType="Inspection" />
    <runner runType="Ipr" />
    <runner runType="JPS" />
    <runner runType="Maven2" />
    <runner runType="rake-runner" />
    <runner runType="simpleRunner" />
  </availableRunners>
  <availableVcs>
    <vcs name="perforce" />
    <vcs name="mercurial" />
    <vcs name="jetbrains.git" />
    <vcs name="svn" />
    <vcs name="cvs" />
  </availableVcs>
  <buildParameters>
    <param name="env.COLORTERM" value="gnome-terminal" />
    <param name="env.COMP_WORDBREAKS"><![CDATA["'><;|]]></value></param></params></methodCall> 

Only once have I been able to restart the agent and have it connect again properly. Generally, I can install it, have it run once, then restarting it gives this error. Any ideas?

It looks like the formatting of the COMP_WORDBREAKS environment variable was messing with the xml structure and not allowing the complete generation of the xml request message.

The COMP_WORDBREAKS value on my machine is "'><;|&(:. Placing the following line in the buildAgent.properties file fixed this problem and allows the agent to properly register.

env.COMP_WORDBREAKS=

I don't see any side-effects yet of making this change; the agent now seems to behave properly.