Defined Default field for sorting children option has no effect on new created ContentObject of said ContentType and is always set to "Content Name - Ascending". After creating Content Object "Sub-items sorting order" can be changed in the "Details" tab.

Steps to reproduce:
1. Clean installation of eZ Platform 2.2
2. Create new Content Type named "Test Content Type", set Default field for sorting children to Location Priority and save it.
3. Create a new Content Object of "Test Content Type" type. Publish it.
4. Go to the "Details" tab of the newly created Content Object.

Result
In "Sub-items sorting order" section you will see that sub-items are ordered by "Content Name", not "Location Priority".