By default, the option Inserted projects are calculated like summary tasks is selected in Microsoft Project.
In other words, the critical path in Microsoft Project will be calculated for the overall master project, not each subproject on its own as shown in the following illustration:
When the option Inserted projects are calculated like summary tasks is not selected, the critical path is calculated for each individual subproject as shown in the following illustration:
Option Location: Schedule page of the Project Options dialog box
Applies to: Microsoft Project, all versions