New IntraCompany rule not working for payments?

We set up a new IntraCompany rule, like this:

If debiting balancing segment A and crediting balancing segment B, use account X If debiting balancing segment B and crediting balancing segment A, use account Y

Otherwise, use account Z

When AP ran payments, they all used account Z, even though the journal batches debited A and credited B and touched no other balancing segment. Other sources such as Cost Management and Projects, used account X and Y where appropriate.

Why would the new rule not work for Payments while it did work for other sources?