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:

java.lang.IllegalArgumentException: A job with this name could not be found: test:b
	at hudson.plugins.jobConfigHistory.JobConfigHistoryBaseAction.getConfigXml(JobConfigHistoryBaseAction.java:163)
	at hudson.plugins.jobConfigHistory.JobConfigHistoryBaseAction.getDiffFile(JobConfigHistoryBaseAction.java:300)
	at hudson.plugins.jobConfigHistory.JobConfigHistoryBaseAction.getDiffLines(JobConfigHistoryBaseAction.java:316)

Seems like you fail to use getItemByFullName correctly.