I've got a combobox on a winforms app with this code:

        comboBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
        comboBox1.AutoCompleteSource = AutoCompleteSource.ListItems;

        DataTable t = new DataTable();
        t.Columns.Add("ID", typeof(int));
        t.Columns.Add("Display", typeof(string));

        for (int i = 1; i < 2000; i++)
        {
            t.Rows.Add(i, i.ToString("N0"));
        }

        comboBox1.DataSource = t;
        comboBox1.ValueMember = "ID";
        comboBox1.DisplayMember = "Display";

I then follow these steps when the window opens:

1. Click the combobox drop down button -- this displays the list of items and selects the text in the combobox
2. Type '5', '1' ... i.e. I'm looking to use autocomplete to search for 515, 516, etc.
3. You'll see that the autocomplete window now appears ON TOP of the drop down list. However if I mouse over, it's the obscured drop down window behind the autocomplete window that's receiving the mouse events, including the click. So I think I'm clicking on an autocomplete item but actually clicking on something totally random that I can't see.

Is this a bug in the ComboBox? I'm using Windows 7 if that matters. Am I configuring the ComboBox wrong somehow?

Note also that using the KEYBOARD uses the autocomplete drop down. So up/down arrow keys are using the front window, but the mouse is using the back window.