Take a look at this code. It gets the "Paris" droplist option that is defined with an initial value of "2" in the "combobox.xml" and it resets the value to "0" using the server-side "PageLoad" event:
Note that the selectedvalue set takes a string value, not an integer.
It is an old post, but it helps someone else, this happened to me but was because I had EnableAutomaticLoadOnDemand set to true, so the items did not exists until the controls was clickced