(I had been loading the user control dynamically using LoadControl, but that turned out to be not relevant.)
Now, within a user control, suppose I have a wee label and an ineffectual button:
<asp:label id="saver" runat="server" />
<asp:button id="Button1" runat="server" text="Go" />
If the label is set using an embedded code block
<% if (!IsPostBack) saver.Text = "Am I saved"; %>
then it is not preserved/shown after the "Go" button has been pressed.
However, if it is set in Page_Load then the label text is shown correctly after "Go" is pressed.
protected void Page_Load(object sender, EventArgs e)
saver.Text = "Am I saved";