Content Type 'Gone Missing' In Views

An unusual post judging that I have looked extensively and not found any reference to this happening before:

I have several content types on a site: blog, event, forum, etc. I had a view which simply was a page, full node view or blog and forum posts but which excluded a variety of other content types.

Recently when editing that view I noticed the option of 'blog' had disappeared. Just vanished. The output of the view was unchanged (i.e. blog posts were still displayed in the view). I cleared the views cache as well as the site cache. That caused the view (without editing it at any point) to stop including posts of the content type 'blog'. 'Blog' content type posts still function throughout the rest of the site - they can be added, commented upon, flagged, etc. Interestingly, when I edited the view from 'include blog and forum content types' to 'exclude event, page, etc (everything not of the blog or forum content type) the view returns posts for the blog and forum content type.

The same behaviour, ignoring blog content type, is common across views, for new views, and having repeatedly cleared both views and site caches.

This can be worked around to an extent, but has made my exposed filters much less user friendly. Checking and unchecking the the module's activation on /admin/build/modules does nothing. Is there any way to completely reset views - delete it's entire existence (full uninstall, rather than just removing and replacing the PHP files) - to see if this helps?