After upgrade to the mentioned versions, I got a lot of logs like this:

Sep 7, 2010 5:08:23 PM hudson.ExtensionFinder$Sezpoz find
WARNING: Failed to load hudson.plugins.cppunit.CppUnitPluginType$DescriptorImpl
java.lang.InstantiationException: java.lang.NoClassDefFoundError: com/thalesgroup/dtkit/metrics/api/InputMetricXSL

I then noticed that all of my CppUnit configurations (in job's configure page) were empty. Not missing, though, because I had to delete the empty entry before I could save an updated configuration.
A bit further down in the console output of the Hudson server I noticed:

Sep 7, 2010 5:34:53 PM hudson.model.Descriptor verifyNewInstance
WARNING: Father of com.thalesgroup.dtkit.metrics.hudson.model.CppUnitHudsonTestType@d8a125 and its getDescriptor() points to two different instances. Probably malplaced @Extension. See http://hudson.361315.n4.nabble.com/Help-Hint-needed-Post-build-action-doesn-t-stay-activated-td2308833.html

A diff on the config.xml files before and after the update shows this:

20c20
< <hudson.plugins.cppunit.CppUnitType>
—
> <com.thalesgroup.dtkit.metrics.hudson.model.CppUnitHudsonTestType>
23,24c23,24
< <deleteJUnitFiles>true</deleteJUnitFiles>
< </hudson.plugins.cppunit.CppUnitType>
—
> <deleteOutputFiles>true</deleteOutputFiles>
> </com.thalesgroup.dtkit.metrics.hudson.model.CppUnitHudsonTestType>

I'm glad this was on a test server, because I'm not going to update all my jobs manually in order to keep a working CppUnit setup ... which is why I've marked this as "Blocker".