CRM 2013 has a new feature that allows displaying Posts, Notes and Activities within a single control (using the Updated Forms). We can easily add this new control to the form by clicking on the Notes ribbon icon on the Insert Tab of the Form Customization.
It seems that the behavior of adding the Notes control is not always the same, as sometimes the control might display only Notes and sometimes it will display the Posts, Notes and Activities.
The solution as to what the control will display can be modified, by exporting the entity, and modifying the FormXml section of the Entity within the customizations.xml file. Within the FormXml section, under forms type = “main”/systemform there is an element called FormPresentation.
The value of FormPresentation can be either 0 or 1. If the value is 0, only the Notes section will appear (classic). If the value is 1, the Posts, Notes and Activities sections will appear (updated). Make the required changes, re-import your entity/solution and publish your customizations and your form will display the Notes control in the proper way.