It seems to be just a "cosmetic" bug.
I have just installed the Plugin Updater for the first time.
Now Plugin Updater gives me the info a new version for Plugin Updater is available (v1.1.3). Even if i click update and restart calibre, the update is still available. Take a look at the attached ss.
I don't think there is a version 1.1.3 available yet, so this seems to be some kind of bug.
Info:
Calibre 0.7.54; Plugin Updater v1.1.2; Windows 7 SP2 x64 all updates installed; UAC with admin rights;