domain mapping and login question

I'm seeing a weird issue that may or may not be related to domain mapping...

I have users complaining of being logged in on one tab and not logged in a second tab.

This is only an issue with mapped domains.

I've tried several different combinations of settings in the domain mapping plugin and I guess I'm just not getting it.

Here's one scenario that I'm seeing:
a user with a mapped domain is logged in to their administration area and editing a post. They click preview to preview the post and they get a 404 error.

Here is what the edit post tab window looks like after hitting the preview button:
http://screencast.com/t/kuamiAVvINH

And here is what the preview tab window looks like: http://screencast.com/t/UygQAZwaJ4

Here's a second scenario:
A user is logged in to their administration area with a second tab open to preview the published changes on the mapped domain.

The user seems to be logged in separately to the mapped and unmapped tabs - to truly be logged out, they have to log out (or in) to BOTH the mapped and unmapped domain.

I guess I just need some one to explain to me exactly what I should be seeing with the various settings in the domain mapping plugin. I looked at the user guide but it does not cover the scenarios above.

Thanks!