multi domains plugin : multi-domain & single signon feature EDIT

Hi there,
I have a question about multi-domains, because either I misunderstood something, or there is something not working as expected.
first thing, if you read some of my past posts here, I'm NOT using Networks+ on that site, AND I have now the dedicated IP for that install.

now, I listed some synonym domains in the multi-domains admin, and set 1 to be public, I want to allow users to registers sites only to that one, and set 8 other domains to private (including the main domain) I want to add users to those only by myself (add people to correct domains depending on manual choice, anyway).

I'm on the test phase with WP multisite + buddypress + some plugins, among which Multi-domains and domain mapping, all versions up to date, sunrise used is the dm-sunrise version

2 issues :

FORGET IT : <strike>1- on the first registration, user can choose if he also want to create a blog, then it's working and only my public domain appears, BUT if the user is already registered and want to create another blog, there is the issues : all the domains are listed there even the ones mentioned as private, </strike> FORGET THAT : I'm STUPID ;O) (I forgot to test with a normal account and tested with my admin account, of course all the domains are available !)

1. and the chosen domain (in the drop-down) does appear in the radio button choice further down instead of the yes/no answer if the user want his site to appear on search engines

2. single sign-on.... if a user is connected on one of those domains, I would expect he's also connected to any of the others listed in the multi-domain plugin, as I have single sign-on activated. I saw other threads about this but no solution there. Is that right it should work like that? Or I misunderstood single sign-on feature?

thank you very much in advance for your help
Cheers
Patricia