When you attempt to send a test message in ListManager you notice that the To address is a real recipient rather than the qualifier for the segment. You have set Utilities > Administration > Server Settings > Advanced, Enable Features tab option for Use Real Recipient Address When Merging Test Messages to No and want to know why you see a real recipient.
This is a bug that has been identified in ListManager versions 12.4 and 12.4.1. Our engineering team is aware of the issue. Information on a solution or updated version to resolve this issue will be published as soon as it is available.
Note that this is the expected behavior when Use Real Recipient Address When Merging Test Messages is set to 'Yes' but is only a simulation and will not send the test message to the recipient shown as explained in the Why do test messages display a real member email address in the "To" field? article.