Approval Groups and Vacation Rules

At our client, we have noticed something unusual. We are interested to know if this is expected and if yes, what is the recommended solution.

At our client, for Interal Supplier Registrations - all requests go to 1 singular approval group. In this approval group, we have Person A and Person B. When a registration request comes in, it normally goes to both Person A and Person B, and the first responder wins.

However, Person A has now set up a vacation rule, which reassigns all approvals to Person B. Now this is breaking the approval workflow with an unexplained error.