Why do some of the events on my page fire twice

This is probably because you explicitly subscribed to the events in code and also specified the AutoEventWireUp of Page to true (it’s true by default). If so, the Page_Load, for example, will be fired once for your event subscription and once because the Page subscribed it for you (by looking for a specific event handler method signature).

To avoid this turn off AutoEventWireUp or remove your subscription code.