Section header in ListView not show correctly

Question

This question is the same as my another question http://stackoverflow.com/questions/3648840/listview-with-section-header-problem
When scrolling the ListView, some header text will appear, below are the related code for easier understanding:

records.setViewBinder(new SimpleCursorAdapter.ViewBinder() {
   public boolean setViewValue(View view, Cursor cursor,int columnIndex) {

        if (columnIndex == dateIndex) {
            //get the record date 
            dateString = cursor.getString(columnIndex);
            //first record or different date records show date title
            if(titleSet.equals(dateString) ||!prevDate.equals(dateString) ){
                 ((TextView) view).setText(dateString);
                 view.setVisibility(View.VISIBLE);
                 prevDate = dateString;
            }else {
                //same day record not show title
                ((TextView) view).setText("");
                view.setVisibility(View.GONE);
            }       
                return true;
            } 

The problem lies on prevDate = dateString. While scrolling, the dateString will change so that preDate will not be accurate as well. So is there anyway I can fix dateString after ListView created? Or to prevent the dateString change out of order? Thanks!