please clear cache in host settings and restart application.

Generally when you have an issue like this, it's because you have both the www and non-www versions of the domain name (or just the domain.com version) in the list of portal alias.  Some modules and functions get the first alias in the list (there is no concept of a 'default' portal alias, although some code treats the first alias as a default).  I'm guessing that either you have a link somewhere that references the domain.com version, or something in the logout or https switch is changing it.

I would suggest you setup your site to always redirect to the www version (if that's what you use), which will not only fix this issue for you, but will also help with your search engine rankings by eliminating duplicate content (if you're interested in search rankings, that is).   I distribute a module which can help with this, or there are other ways to set it up as well.

You said "something in the logout or https switch is changing it" -- Do you know if that is fixable and if so, how to do so?