Behaviour observed:

The dropdown-list for the JVM auto-install is empty, no JVM can be selected. See jvm_autoinstall.png.
Of course, auto-install can't be done with no JVM selected.

Some more details:

The file Jenkins\updates\hudson.tools.JDKInstaller contains:

{"jdks": [{"name": "JDK 6", "list": []}, {"name": "JDK 5.0", "list": []}, {"name": "JDK 1.4", "list": []}]}

Jenkins' request to update the file:
http://updates.jenkins-ci.org/updates/hudson.tools.JDKInstaller.json?version=1.418
gives a 302 redirect to
http://mirrors.jenkins-ci.org/updates/updates/hudson.tools.JDKInstaller.json?version=1.418
but that's also empty:

downloadService.post('hudson.tools.JDKInstaller',{"jdks":[{"name":"JDK 6","list":[]},{"name":"JDK 5.0","list":[]},{"name":"JDK 1.4","list":[]}]})

Behaviour expected:

If the update list from the server is empty, a valid selection should still be available.