If you go to a module, say Contacts for example, you can choose Import Contacts from the top. When doing that, it lets you assign contact owners using either the users email address or their user id number (found in the URL of their user screen).  You can even use assignment rules. All of this functionality works fine.

However, if you go to Settings > Import, none of the options work. You can map the users email address or their user ID to the "Contact Owner ID" field and it just ignores it and assigns it to the user doing the import.