Missing toolbar -- but it shows on a cloned site

So I have a puzzler that is general in nature but is on a multisite deployment with the dev dashboard.

I have a site on the network that refuses to show the front end toolbar to a logged in user (everything fine in the back...). I can manually force the toolbar to show for everyone and then the band appears -- but is empty except for the Home icon. I cloned this site to a test site and the toolbar appears fine on that one. Everything seems identical, all configuration items identical EXCEPT that my clone is not mapped to a domain. Is there anything in the the domain mapping that might be preventing the broken site from recognizing the logged in user?