UpdatePanel on masterpage does postback on first button click

I have an update panel on a masterpage and for reasons unbeknown to me our content placeholder is within the updatepanel. But when I click on a button on one of our pages that uses the masterpage the 开发者_开发知识库page postsback. If I then click the button for a second time it does not postback and does an ajax call. Im wondering why it does a postback the first time when I dont want it to. Below is how I have the updatepanel set up

Make sure all trigger controls have valid ID.