The default home page settings offers three alternatives: Site, MyMoodle (should be 'MyHome') and Uer preferences. User preferences opens the profile page after first login and the site. During second login user is led to site.

The idea behind user preferences settings seems that a new user should make settings in his profile while logging in the first time.

Due to the combination of User preferences with Site as next page its not possible to define User preferences aduring first login and afterwards MyHome.

It seams to be sensefull notto combine Site/MyHome with User preferences and to add User opreferences as seperate configuration element.