Hi Simon,
Following on from Matt, I can confirm this behaviour is as implemented in v1.1.1 of the framework.
The menu completion bar is based upon all of it's children components.
The page completion bar is measured according to all of the components explicitly included using the pagelevelprogress properties.
Therefore you must complete everything on the page for the menu to appear complete but only those included explicitly for the page to appear complete. To avoid this difference you should include all of your components in the pageLevelProgress for v1.1.1.
Alternatively you can log an issue at https://github.com/adaptlearning/adapt-contrib-pageLevelProgress/issues if you'd like this behavior changed, however, as v2 is just about to arrive, and having personally spent a great deal of time working to sort out this issue in v2, i know it's quite big change, so I'm not sure if a fix is likely to happen for v1.1.1 any time soon or even at all (this fix is kinda a 'breaking' one in some respects as it introduces a raft of new features).
I would suggest either the above solution (including everything), turning off plp entirely for that page, or holding off for v2 where this issue is fixed.
I hope that helps.
Ollie.