1 If there is more than one option in the Page Location drop down box when create a new page, when you preview, all other options are removed and you can only select your original selection.
3 The problem exists on Ikiwiki's wiki, but manifests itself differently, in that subpages are still displayed, so maybe that's the actual bug :)
5 Anyway, to reproduce, edit any page, view the page location options, preview, and some will disappear.