Check all the settings for that Fully Hosted Domain.
I just had some problems today while changing settings. Maybe the Panel doesn't like Safari, but when I'd change one domain, it'd inherit some of the settings of another domain I modified, such as owner (and subsequently the user directory) and the domain directory.
If that doesn't work, set it to redirect to some other domain, wait a while for that to take effect, then switch it back to Fully Hosted with the appropriate settings.
Or just contact Support.