Launching an event from a dropdownlist in a gridview while editing

[katmagic]

I have added a dropdownlist to the <EditItemtemplate> portion of a gridview,
and I want to capture the event when a user selects an item in the drop down
list. I have added to the dropdownlist properties AutoPostback = true, and
all of the following
OnSelectIndexChanging="DropdownListCustomers_SelectedIndexChanged"
OnSelectedIndexChanged="DropdownListCustomers_SelectedIndexChanged"
OnTextChanged="DropdownListCustomers_SelectedIndexChanged"

No matter what I do, DropDownListCustomers_SelectedIndexChanged does not get
launched. How would I capture when a user changes this dropdownlist?