Module config.xml files were confusingly starting with <maven2-module-set> (as distinct from <maven2-moduleset> for the top-level config.xml).
This was the old mistaken value which we need to be able to *read* but should never *write*.
Every time you call XStream.alias, you are setting the new default element name for saving,
yet the code was mistakenly setting the compatibility alias after the desired alias.