I renamed a job yesterday on 1.491 and this morning, Jenkins showed it as having no builds - even though I could see them on the file system.
Immediately after the renaming, Jenkins seemed to have "lost sight" of the existing workspace. So I fired another build and all was good. But this morning, it had "forgotten" both that build and the workspace again.
Restarting Jenkins seems to have fixed it.
(Hope I picked the right component...)