GroupBy property is not working

I´m using a GRID to show some data and I’m using the createdOn field that axelor creates by default to each entity but is not ordering the data based on tha field.

this is my grid:

<grid name="policy-new-notes-grid-policy-info" title="Notes" model="com.vumi.policy.db.PolNotes" orderBy="createdOn"
		  canNew="false" canEdit="false" edit-icon="false" x-row-height="160">
		<button name="editNote" onClick="action-can-edit-note,action-view-edit-note" icon="fa-pencil"/>
		<button name="showNote" onClick="action-view-edit-note_search" icon="fa-file-text-o"/>
		<field name="notifyClaim" title="Notify in Claims"/>
		<field name="notesTypeId" title="Type" readonly="true" width="100"/>
		<field name="noteNotes" title="Description" readonly="true" width="400"/>
		<field name="createdBy" title="User" readonly="true"/>
		<field name="createdOn" title="Created On" readonly="true"/>

and this is how the view is showing the data:

what could be the reason that not order the data, I’m missing some configuration?