I would like someone else to confirm this: there seems to be a bug with the list of transcluded templates which appears at the bottom of the edit view.

If you create a template which uses <includeonly> and inside that tag you transclude another template, that second template does not appear on the list of templates. It does however seem to appear OK on the list for client pages, i.e. those which transclude the "outer" template.

HTH HAND