I don't know it they have fixed it, but remember that when I was working on .NET v1.1, both DropDownList and select tag won't work.
I have to implement select tag then explicitly write any <submit button>.click() on onchange event. (Apparently the SelectedIndexChanged event has been queued in the postback metadata, just that postback somehow not triggered. The event handler will run the event on the next postback occurred)
Just remember that you MUST turn off AutoEventWireup in order to use this workaround.
I'm not sure I understand your solution. You mean that the event will fire once a postback occurs, but that you have to insert a seperate submit field to invoke the postback?