Domains, links, bug in Wordpress?

I'm having a weird problem with my network. I have 5 or 6 sites, 3 of which have a mapped domain.

For two of them, if you use the super-admin bar, and go to MySites > NameofSite > VisitSite, you will go to the site as http://www.nameofsite.com, and it will not show the admin bar.

For the other one, you will go to http://www.mainsite.com/nameofsite and it WILL have an admin bar.

Not sure why there is a difference in the admin bars, but I would think it should show up on all 3.

While on that third site, if you click on a post, then on Edit Post, then make an edit (or don't), and go to View Post (from the admin bar) you won't go back to the live post, you will go to the main site. Not 3rd-site.com, or even mainsite.com/3rd-site, but the network's main site - mainsite.com. Same if you go to Visit Site from the admin bar under that site's name.

Actually, I just went from the super-admin bar to the site, to Visit site, and it went to the main site this time, instead of to the subsite. It usually goes to mainsite.com/3rd-site.

My ISP says it's a bug in Wordpress.

Also, my ISP set up the domain mapping for the 2 that work right (except for no admin bar on the front end), I set it up, according to their instructions, for the one the 3rd site. I'm wondering if I made the wrong choice for mapping. They were:

disabled and entered domain should be used
directed to mapped (primary) domain
directed to original domain

I used the default, which I don't really remember, but I think it was the first choice.

I also wonder about going to the first 2 sites and not having an admin bar showing for them.

Is this something with the domain mapping plugin, my mapping choice, or should I go to Wordpress with it? And has anyone else had these issues?

Thanks for any advice!