Calendar inside UpdatePanel not working as Trigger with Master page

I got 2 test pages: one with Master page and second empty.
The empty one looks like this:
<asp:ScriptManager ID="scriptManager" runat="server" /> <asp:UpdatePanel ID="calendarUpdatePanel" runat="server" UpdateMode="Conditional"> <ContentTemplate> <asp:Calendar ID="calendar" runat="server" /> </ContentTemplate> </asp:UpdatePanel> <asp:UpdatePanel ID="timetableUpdatePanel" runat="server" UpdateMode="Conditional"> <ContentTemplate> <asp:PlaceHolder ID="placeHolder" runat="server" /> </ContentTemplate> <Triggers> <asp:AsyncPostBackTrigger ControlID="Calendar" EventName="SelectionChanged" /> </Triggers> </asp:UpdatePanel> When user selects Date from Calendar ...