The change event is being triggered when having an initially selected item in the DropDownList and then open the DropDownList and click on the default selected item. This bug is represented only in MVVM.
The change event of a DropDownList with initial data selected is being triggered when clicking on the already selected value.
Selecting the already selected item of a DropDownList shouldn't trigger its change event because there is no actual change in the component's value. Please check this Dojo for the expected behavior.