I found the following behavior:
1) I have two groups: group1 and group2
2) I created a Data Partition with the following constraint:
Call_Req, View, NOT(group.last_name IN('group1'))
and attached it to a contact.
3) I created 3 requests:
CR1 with group1 attached
CR2 with group2 attached
CR3 with no group attached.
4) If now the contact with the new DP attached searches for requests I would expect to see CR2 and CR3. CR1 is not visible due the restriction. But the contact sees only CR2.
CR3 with the empty group is not visible. Is this by design?