Q: When I append text to the end of the current content of a multiline listbox, it is always scrolled back to the first line. Even if I later use ScrollToCaret to return to the end of the text, the whole control briefly flickers. Is there a way to avoid it?

A: Indeed there seems to be an issue in Compact Framework where replacing selection in an edit control. Apparently someone wanted to be clever and even though there is a dedicated control message EM_REPLACESEL, he implemented set_SelectedText in the following way:

string SelectedText
{
    get
    {
        if ( SelectionLength == 0 )
            return "";
        return new string(Text.ToCharArray(), SelectionStart, SelectionLength);
    }
    set
    {
        this.Text = this.Text.Remove(SelectionStart, SelectionLength).Insert(SelectionStart, value);
        SelectionStart = this.Text.Length;
        SelectionLength = 0;
    }
}
 

Why is it done this way, I don't know. There are perfectly good tools at the edit control message level to work with selection. What's important here is that set_SelectedText internally calls Control.set_Text which translates into WM_SETTEXT message. In case of an edit control it has a side effect of moving caret to the beginning and scrolling the text to the same place, thus creating an unpleasant flicker.

To remedy this problem we simply replace set_SelectedText with our own implementation:

You will also need the following PInvoke definitions:
 
const uint EM_REPLACESEL = 0xc2;
[DllImport("coredll")]
extern static IntPtr GetCapture();
[DllImport("coredll")]
extern static int SendMessage(IntPtr hWnd, uint Msg, bool WParam, string LParam);
 
To get HWND of your textbox use something like this:
 
private IntPtr GetHWND(Control ctl)
{
    ctl.Capture = true;
    IntPtr hWnd = GetCapture();
    ctl.Capture = false;
    return hWnd;
}