ComboBox SelectedIndexChanged fire for every INotifyPropertyChanged

.Net 4.5 Windows Forms

I have a strange problem.

• I inherit from a BindingList and the items support the INotifyPropertyChanged interface.
• I assign the list to a combo box DataSource property.
• I assign a handler to the combo box SelectedIndexChanged event.

Now, whenever an item property value changes the selectedindex changed event of the combo box fires, regardless whether or not the index changed.

Why?