Demand Priority Rule is error when certain combinations are set in Backlog Management

Summary:

An error occurs when the following settings are attempted for a particular demand priority rule.

■Error Case1
Rank 1 - Customer Name
Rank 2 - Customer Name

■Error Case2
Rank 1 - Order Type
Rank 2 - Order Type

Error message :“You must add an attribute supported in the Backlog Management work area because this rule is selected in that work area"
The following configuration succeeds.

■Success case1
Rank 1 - Order Type
Rank 2 - Customer Name

■Success case2
Rank 1 - Customer Name
Rank 2 - Order Type

What I don't understand is that the Error Case 1 and 2 settings do not cause errors in other Demand Priority rules.