User blog comment:Rappy 4187/Technical Update: December 7, 2015/@comment-24473195-20151209160356/@comment-118323-20151209172831

If a template type is already set, then the dialog should not display during the edit session. The dialog should only remind you upon creating a brand-new template or saving a template classified as "unknown".

And yes, we want to improve Special:Templates in the near future.