Hi Wentsi,
Try following my instructions below and let me know how it goes. I have tested the same on the stock Customer List screen with success.
Click Edit to enter the Grid Wizard for Contacts and go to Step 3:Filters.
Ensure 'Choose or create a View Name' is set to your default view - this is Shared Active Customer Contacts on the stock screen.
From 'Choose from a list of available fields' select SpecialType.
Filter: 'Contains' will include Contacts and AltContacts. 'Equal to' will only show Contacts.
Get value from: Type In
Select value: Contact
These steps should produce the desired result.
Noel