CListBox jitter.

The way I am using a CListBox causes the list box contents to jitter. I
think two of the things I am doing causes this problem. Is there is a way to
stop this?

Here is what I'm doing:

Please understand that in my program, at any time, a background process may
add a new line to the top of the list box. Normally if you are scrolled down
somewhere looking at some other line, when the background process adds the
new line, the list box jumps to the top. The user becomes frustrated because
he was looking at something important and it jumped away from him. So I want
to keep the list box displaying the same text lines even if new data is
added at the top

I added a new insert function in my CListBox subclass. The background
process uses this to add a new string to the top:

IndexTop = GetTopIndex();
InsertString(0, Text);
if (IndexTop != LB_ERR)
{
    // check if the list box is NOT displaying the top entry
    if (IndexTop != 0)
    {
        // don't scroll the screen
        SetTopIndex(IndexTop + 1);
    }
}

The problem is that when a new string is added, the screen jumps to the top.
The code then places the window back to where it was before. On some
computers there a VERY noticeable jitter. And a ghost image of the top
lines.

I also have the need to sometimes replace text on a line within the
CListBox. CListBox doesn't have a ReplaceString function. My subclass
function replaces the text by first deleting the line at whatever provided
index and then adding a new line with the new text at that same provided
index. But, unfortunately, of the background process does this and you are
scrolled someplace else, there is jitter.

HOW CAN I STOP THE JITTER?