Proč by to nefungovalo správně?

            var selectionStart = richTextBox1.SelectionStart;
            var found = richTextBox1.Find("tempus");
            if (found != -1)
            {
                int start;
                int length;
                if (selectionStart < found)
                {
                    start = selectionStart;
                    length = found - start;
                }
                else
                {
                    start = found;
                    length = selectionStart - start;
                }
                richTextBox1.Text = richTextBox1.Text.Remove(start, length);
            }