administrator doesn’t have authoring privileges in multi-user applications

I added “author” and “contributor” permissions to several users of my blog; as long as “nikflorida” (the administrator) was the only one posting items, there was no problem, but as soon as there were several options for “author” of a post, “nikflorida” was no longer one of those options. A new account called “-nikflorida” with privileges set to “editor” turned out to be a suitable workaround, but “nikflorida” (the administrator) does not appear in the drop-down for authors, and posts created by “nikflorida” are attributed to the first username alphabetically with posting privileges. What’s up with that?

I am, of course, using the latest updates of WP and the Atahualpa theme on https://NikFlorida.org. But this occurs in any theme I have tried, including the WP default theme. Thoughts?