ASP UpdatePanel Trigger causing full page postback

I have two drop down lists where one is inside an update panel and the other is outside.When the Index is changed on ddlFaculty the whole page is postedback instead of a partial for the contents in the update panel.
I have read in the ASP docs that sometime validation controls bog down update panels but im not too sure if thats the problem here.

<div class="form-group"> <asp:Label runat="server" AssociatedControlID="ddlFaculty" CssClass="col-md-2 control-label">Faculty</asp:Label> <div class="col-md-10"> <asp:DropDownList ID="ddlFaculty" EnableViewState="true" class="form-control" runat="server" aria-expanded="true" ValidationGroup="g4" SelectedIndexChanged="ddlFaculty_SelectedIndexChanged"> <asp:ListItem Value="null ...