Calendar page's mlid changes when the module is disabled, then re-enabled

We noticed that whenever we disable the Calendar module (which is sometimes required when making updates to Drupal), the menu-link id (mlid) assigned to the Calendar page is different after we re-enable the module. This causes the calendar's sub-navigation links to get orphaned; and any references that we have to that mlid (such as in CSS files) then need to be updated.

Is this unusual behavior? Is there some way we can keep the mlid from changing whenever the Calendar module is disabled and then re-enabled?

Thank you for your time and help.