The GridViewCheckBoxColumn.EditMode property controls when the value of the editor will be submitted to the cell. By default, the value is OnValidate and the value will be submitted only when the current cell changes, the grid looses focus or the active editor is closed by pressing Enter. If you set the EditMode property to OnValueChange it will submit the value immediately after the editor value changes. Please refer to the attached gif files illustrating the difference between the two modes.

To reproduce: if you set the GridViewCheckBoxColumn.EnableHeaderCheckBox property to true, the cell value is always submitted immediately after toggle/untoggle the checkbox without considering that EditMode.OnValidate is used.