I've reverted a number of recent commits to the Title class which added several more pre-cached fields to it, as I really don't think we want that sort of data in Title objects to begin with. A Title object is meant to represent a... well, a page title :) and as such should be roughly equivalent to passing the string-form title around, but without having to parse and de-parse the items all the time.
Since ancient times we've had a couple things like an article ID being saved into local state, which is frequently useful to optimize lookups but has its own problems (it has to be explicitly cleared or reset from time to time). These really belong more in a 'Page' object than a 'Title' however.
These days we've got a WikiPage class which has been further split from Article as well; it seems to me that these sorts of things might belong better there than in Title. Thoughts?
-- brion