In Negotiation Approvals, operator "Is not in" is missing when "Category name" is selected

Content

I have posted this issue as a SR and it was closed as intended behavior.

But I'm not convinced, so I post it here.

[What is an issue?]

In Negotiation Approvals, operator "Is not in" is not available when "Category name" is selected as the condition attribute. You can select "Is in" operator. But you cannot select "Is not in" operator.
Shouldn't "Is in" and "Is not in" operators be available as a set?

In case of Purchasing Approvals and Requisition Approvals, 

operator "Is not in" is available when "Category name" is selected as the condition attribute.

 

[What does happen if it is not fixed?]