Problem with Vacation Rule and AP invoice approval, item_type gets stuck

Dear all,

We are running into a problem with an AP Invoice when user add a vacation rule to a person who is in the same hierarchy.

The approval is handled in AME.

This is the first case.

Without the vacation rule the approval list would be:

Approver A

Approver B

The problem occurs when Approver A creates a vacation rule and delegates response to Approver B.

AP approval is initiated and the notification to Approver A is delegated to Approver B, who can approve the notification and the approval seems to be completed succesfull.

Unfortunately this is not the case, for activity 'Invoice Approval Process'  get stuck and ends with activity result '#STUCK'.