When adding an Employee to the list of owners ("Owners" tab) for a service item in IT Shop, this is not updating the group owner or the service item owner, although it appears that way in IT Shop, as it shows as "Group owners".
When you add owners this way, you are actually adding the UID_Person for that Employee to the existing role, the Product owner. These are the Employees listed under "Assigned". Thus, wherever the role itself is assigned, you will see any Employees assigned that role.
In the image below, the service item has Product owner, 'Test1, Employee', and assigned Employees are listed:
The query is UID_Person in (select UID_Person from PersonInAERole where UID_AERole = '%UID_OrgRuler%').
UID_OrgRuler is the product owner for the service item. This is a role, and thus can be assigned to multiple Employees, just like any other role.
A service item can have only one owner, which is the role. If you want to keep one owner per service item, you would have to create individual roles for each user.