Seems that JobConfigHistory.isSaveable assumes any AbstractProject should be saved. This makes sense for a MavenModuleSet but rarely makes sense for a MavenModule. I think you should only save a TopLevelItem (at least by default); otherwise you wind up saving tons of config records for things which users rarely if ever save changes to.
BTW showing config changes to a Maven module does not even work, though they are recorded:
Seems like you fail to use getItemByFullName correctly.