Android : onitemclick disappears when back button is pressed

I have a listview which is in single choice mode. When I click on the item in the listview a button is displayed on the listview position. This button disappears when I press back button or Ok button. I want it to be saved until the next onitemclick.

I have included only the oncreate, getview and onitemclick methods in adapter

public class ExpiredActivity extends Activity implements View.OnClickListener { private final static String TAG = "ExpiredActivity";

private ListView mExpiredListView;
private Button mButtonDone;
private TextView mTextSummary;
private ExpiredListAdapter mAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_choose_expiry);
    getActionBar().hide();
    mExpiredListView = (ListView) findViewById(R.id.system_list);
    mButtonDone = (Button) findViewById(R.id.button_done);
    mTextSummary = (TextView) findViewById(R.id.text_summary);
    mButtonDone.setOnClickListener(this);
    mAdapter = new ExpiredListAdapter(getApplicationContext());
    mExpiredListView.setAdapter(mAdapter);
    mExpiredListView.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
    mExpiredListView.setOnItemClickListener(mAdapter);

    private class ExpiredListAdapter extends BaseAdapter implements OnItemClickListener {
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            final LayoutInflater inflater =
                (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.system_list_item, parent, false);
        }

        LogonResponseData.SevInfo item = (LogonResponseData.SevInfo) getItem(position);

        TextView txtName = (TextView) convertView.findViewById(R.id.text_name);
        TextView txtType = (TextView) convertView.findViewById(R.id.text_type);

        txtName.setText("Days");
        txtType.setText("- " + item.value);
        showMointorState(convertView, position);

        return convertView;
    }

    private void showMointorState(View view, int position) {
        CheckBox chk = (CheckBox) view.findViewById(R.id.chk_flag);
            if(mExpiredListView.isItemChecked(position))
            {
                chk.setChecked(true);
            }
            else {
                chk.setChecked(false);
            }
        chk.invalidate();
    }

    @Override
    public void onItemClick(AdapterView<?> adpater, View view,
            int position, long id) {

            mExpiredListView.setItemChecked(position, true);
            showMointorState(view, position);
    }
}

Below is my xml file

activity_choose_expiry

<RelativeLayout 
    android:id="@+id/header"
    android:layout_width="match_parent"
    android:layout_height="45dip"
    android:layout_alignParentTop="true"
    android:layout_marginBottom="10sp"
    >
    <Button 
        android:id="@+id/button_done"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/done"
        android:layout_alignParentRight="true"
        android:background="?light_blue"
        android:textColor="@android:color/white"
        android:textSize="18sp"
        />
    <TextView
        android:id="@+id/text_title"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:layout_toLeftOf="@id/button_done"
        android:text="@string/choose_expiry"
        android:textSize="18sp"
        android:textColor="?default_text"
        />
</RelativeLayout>

<TextView
    android:id="@+id/text_summary"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="14sp"
    android:textColor="?light_blue"
    android:layout_alignParentBottom="true"
    android:gravity="center"
    />

<ListView
    android:id="@+id/system_list"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:dividerHeight="6dp"
    android:divider="#00000000"
    android:layout_above="@id/text_summary"
    android:layout_below="@id/header"
    />

</RelativeLayout>

system_list_item

<CheckBox 
    android:id="@+id/chk_flag"
    android:layout_width="24sp"
    android:layout_height="24sp"
    android:layout_alignParentRight="true"
    android:layout_alignParentTop="true"
    android:button="?ic_tag_blue"
    android:clickable="false"
    android:focusable="false"
    />

<LinearLayout 
    android:id="@+id/left_up"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_toLeftOf="@id/chk_flag"
    >

    <TextView 
        android:id="@+id/text_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginRight="10sp"
        android:textSize="18sp"
        android:textStyle="bold"
        android:textColor="?default_text"
        />

    <TextView 
        android:id="@+id/text_type"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="16sp"
        android:textColor="?default_text"
        />
</LinearLayout>

<TextView 
    android:id="@+id/text_desc"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textSize="12sp"
    android:layout_alignParentLeft="true"
    android:layout_alignParentBottom="true"
    android:layout_toLeftOf="@id/chk_flag"
    android:layout_below="@id/left_up"
    android:textColor="?default_text"
    />

 </RelativeLayout>