Multiple ComboBox on the same page with OnSelectedIndexChanged

I several Combo boxes on the same page, all with OnSelectedIndexChanged set to go to a different page depending on their value.

So I:

1.) Select an item in the first ComboBox and it uses the DataValueField and goes to that page (no problem)

2.) then I hit back on the browser and return to this original page - this selected value is still appearing in the first ComboBox.

3.) Now I select an item from the second ComboBox using a different OnSelectedIndexChanged event and it runs the first ComboBox OnSelectedIndexChanged event and goes to that page instead of the second.

Any suggestions would be great,

Dan