Seems to be the analogue issue to http://issues.jenkins-ci.org/browse/JENKINS-5128

Could you please do 2 things:

• attach the file hudson.plugins.jabber.im.transport.JabberPublisher.xml (of course, you should mask all user names/password in there first)
• try the workaround described in JENKINS-5128 (apply it to hudson.plugins.jabber.im.transport.JabberPublisher.xml of course)

The workaround worked, and here is the config file.

Just noted that next time i restarted Hudson, fields once again went missing.

Just to be clear:
You updated to Hudson 1.339 (BTW: from which previous version?) and you did NOT update the jabber and instant-messaging plugin
and after that the config disappeared?

can't confirm exactly where the config vanished, since I only noticed at a later point. But it was there the day before i updated for sure.

But i did upgrade Hudson first then installed whatever plugin updates were available.

The upgrade was from 1.337.

The config file looks absolutely fine to me.

Is there anything interesting in the log file.
If not, could you try to increase the log level and look again?

Upgraded to 1.341 and restarted, below is the log but there is nothing interesting in it related to this bug, i think.
Log seems to be at highest level.

[Winstone 2010/01/18 19:34:24] - HTTP Listener started: port=8080
[Winstone 2010/01/18 19:34:24] - AJP13 Listener started: port=8009
[Winstone 2010/01/18 19:34:24] - Winstone Servlet Engine v0.9.10 running: controlPort=disabled
18 Jan 2010 7:34:24 PM hudson.model.Hudson$4 onAttained
INFO: Started initialization
18 Jan 2010 7:34:32 PM hudson.model.Hudson$4 onAttained
INFO: Listed all plugins
18 Jan 2010 7:34:42 PM hudson.plugins.im.HudsonIsBusyListener <init>
INFO: Executor busy listener created
18 Jan 2010 7:34:42 PM hudson.model.Hudson$4 onAttained
INFO: Prepared all plugins
18 Jan 2010 7:34:42 PM hudson.model.Hudson$4 onAttained
INFO: Started all plugins
18 Jan 2010 7:34:52 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.web.context.support.StaticWebApplicationContext@3cdfd643: display name [Root WebApplicationContext]; startup date [Mon Jan 18 19:34:52 SAST 2010]; root of context hierarchy
18 Jan 2010 7:34:52 PM org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.web.context.support.StaticWebApplicationContext@3cdfd643]: org.springframework.beans.factory.support.DefaultListableBeanFactory@2a85f3d6
18 Jan 2010 7:34:52 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@2a85f3d6: defining beans [daoAuthenticationProvider,authenticationManager,userDetailsService]; root of factory hierarchy
18 Jan 2010 7:34:56 PM hudson.plugins.dbcharts.DbChartPublisher$DescriptorImpl <init>
INFO: DescriptorImpl constructed
java.io.FileNotFoundException: /usr/lib/jvm/java-6-openjdk/jre/lib/security/cacerts (No such file or directory)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(FileInputStream.java:137)
at java.io.FileInputStream.<init>(FileInputStream.java:96)
at org.jivesoftware.smack.ServerTrustManager.<init>(ServerTrustManager.java:54)
at org.jivesoftware.smack.XMPPConnection.proceedTLSReceived(XMPPConnection.java:1109)
at org.jivesoftware.smack.PacketReader.parsePackets(PacketReader.java:327)
at org.jivesoftware.smack.PacketReader.access$000(PacketReader.java:43)
at org.jivesoftware.smack.PacketReader$1.run(PacketReader.java:63)
18 Jan 2010 7:35:03 PM hudson.plugins.jabber.im.transport.JabberIMConnection connect
INFO: Connected to XMPP on [REMOVED]:5222
java.io.FileNotFoundException: /usr/lib/jvm/java-6-openjdk/jre/lib/security/cacerts (No such file or directory)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(FileInputStream.java:137)
at java.io.FileInputStream.<init>(FileInputStream.java:96)
at org.jivesoftware.smack.ServerTrustManager.<init>(ServerTrustManager.java:54)
at org.jivesoftware.smack.XMPPConnection.proceedTLSReceived(XMPPConnection.java:1109)
at org.jivesoftware.smack.PacketReader.parsePackets(PacketReader.java:327)
at org.jivesoftware.smack.PacketReader.access$000(PacketReader.java:43)
at org.jivesoftware.smack.PacketReader$1.run(PacketReader.java:63)
18 Jan 2010 7:35:07 PM hudson.plugins.jabber.im.transport.JabberIMConnection connect
INFO: Connected to XMPP on [REMOVED]:5222
18 Jan 2010 7:35:11 PM hudson.model.Hudson$4 onAttained
INFO: Loaded all jobs
18 Jan 2010 7:35:13 PM hudson.model.Hudson$4 onAttained
INFO: Completed initialization
18 Jan 2010 7:35:13 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.web.context.support.StaticWebApplicationContext@39df3255: display name [Root WebApplicationContext]; startup date [Mon Jan 18 19:35:13 SAST 2010]; root of context hierarchy
18 Jan 2010 7:35:13 PM org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.web.context.support.StaticWebApplicationContext@39df3255]: org.springframework.beans.factory.support.DefaultListableBeanFactory@6064af0f
18 Jan 2010 7:35:13 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@6064af0f: defining beans [filter,legacy]; root of factory hierarchy
18 Jan 2010 7:35:14 PM hudson.TcpSlaveAgentListener <init>
INFO: JNLP slave agent listener started on TCP port 36443

Are you sure that you are running at the highest log level?
I can only see INFO messages and I would expect FINEST or DEBUG messages - depending on the logging framework in use.