Strange behaviour of checkBox in the listView

I have fragment with a listView, the listview layout contains (TextView, checkBox and ImageView as follows

t1........CB.......IV
t2........CB.......IV
t3........CB.......IV
t4........CB.......IV
t5........CB.......IV
t6........CB.......IV
      SaveButton

in the getView() method, I check if the checkbox is checked or not, and if it is checked, I add the checked items to a list.

the problem is when, initially I set all the checkboxes to be unchecked, but when i check the first item, surprisingly, the third item from below is automatically checked, and if i check the 2nd item from above, the 2nd item from below is checked, and if i check the 3rd item from above , then the last item is checked automatically?!!

please have a look at getView() method and let me know what I missed:

getView():

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub

    if (convertView == null) {
        LayoutInflater layoutinflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        convertView = layoutinflater.inflate(R.layout.list_items_layout, null);
    }

    if (this.checkedItemsList == null) {
        this.checkedItemsList = new ArrayList<String>();
    }

    final TextView tv = (TextView) convertView.findViewById(R.id.tvlist_topic);
    final CheckBox cb = (CheckBox) convertView.findViewById(R.id.cbList_hook);
    final ImageView iv = (ImageView) convertView.findViewById(R.id.ivList_delete);

    tv.setText(this.topicsList.get(position));

    cb.setOnCheckedChangeListener(new OnCheckedChangeListener() {

        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            // TODO Auto-generated method stub
            if (isChecked) {
                checkedItemsList.add(topicsList.get(position));
                setCheckedItemsList(checkedItemsList);
                Log.d(TAG, "size: " + checkedItemsList.size());
            }
        }
    });

    iv.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            if (cb.isChecked())
                cb.setChecked(false);

            topicsList.remove(position);
            notifyDataSetChanged();
        }
    });

    return convertView;
}