Hi Jonathan Simmons,
Thank you for contacting us.
The SelectedIndexChanged event is fired when you are setting the DataSource property. The event triggers if you are setting the ValueMember and DisplayMember after you have assigned the DataSource property. The reason is that the list of items is created each time you are setting these properties. This is the default behavior of the radComboBox.
The only workaround that I can suggest is to use BindingSource and invoke the Fill method after setting the DataSource, DisplayMember and ValueMember properties of the radComboBox. Here is an example:
|this.radComboBox1.DataSource = employeesBindingSource;
|this.radComboBox1.DisplayMember = "LastName";
|this.radComboBox1.ValueMember = "EmployeeID";
Unfortunately, I was not able to produce a workaround for your issue, since you are using a DataTable. If you encounter any other issues, do not hesitate to contact me back.
the Telerik team