Repro steps:

• start with clean installation
• add one slave "slave"
• add multi-configuration job
• select "Add Axis" then select "Slaves"
• select both "master" and "slave"
• save the job

When saving matrix configuration in Internet Explorer exception occurs:

Status Code: 500
Exception:
Stacktrace:
java.lang.RuntimeException: Failed to instantiate class hudson.matrix.LabelAxis from {"":[

{"values":"master"}

,

{"values":"slave"}

],"kind":"hudson.matrix.LabelAxis$DescriptorImpl","name":"label","stapler-class":"hudson.matrix.LabelAxis"}
at hudson.model.Descriptor.newInstance(Descriptor.java:497)
at hudson.model.Descriptor.newInstancesFromHeteroList(Descriptor.java:767)
at hudson.util.DescribableList.rebuildHetero(DescribableList.java:171)
at hudson.matrix.MatrixProject.submit(MatrixProject.java:601)
at hudson.model.Job.doConfigSubmit(Job.java:964)
...

When saving matrix configuration in Firefox 3.6 everything is ok.

Notice that correct instatiation string should be as follows:

{"kind":"hudson.matrix.LabelAxis$DescriptorImpl","name":"label","stapler-class":"hudson.matrix.LabelAxis","values":["master","slave"]}

instead of what we have in Internet Explorer:

{"":[

{"values":"master"}

,

{"values":"slave"}

],"kind":"hudson.matrix.LabelAxis$DescriptorImpl","name":"label","stapler-class":"hudson.matrix.LabelAxis"}