Android - ExpandableListView with checkboxes doesn't work correctly

I implemented ExpandableListView with checkboxes for groups and child items. Here is my code.

filter_group_item.xml (The same in filter_child_item.xml)

<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:id="@+id/text"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        style="@style/MainTheme.BodyText"
        android:paddingLeft="?android:attr/expandableListPreferredItemPaddingLeft"
        android:layout_weight="9"/>
    <CheckBox
        android:id="@+id/check_box"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:focusable="false"/>
</LinearLayout>

ExpandableListAdapter

public class ExpandableListAdapter extends BaseExpandableListAdapter {
private Context context;
private List<String> titles;
private HashMap<String, List<String>> items;
private HashMap<String, Boolean> allItems;

public ExpandableListAdapter(Context context, List<String> titles, HashMap<String,
        List<String>> items, HashMap<String, Boolean> allItems) {
    this.context = context;
    this.titles = titles;
    this.items = items;
    this.allItems = allItems;
}

public List<String> getCheckedItems() {
    List<String> checkedItems = new ArrayList<>();
    for (String item : allItems.keySet()) {
        if (allItems.get(item)) {
            checkedItems.add(item);
        }
    }
    return checkedItems;
}

@Override
public int getGroupCount() {
    return titles.size();
}

@Override
public int getChildrenCount(int groupPos) {
    return items.get(titles.get(groupPos)).size();
}

@Override
public Object getGroup(int groupPos) {
    return titles.get(groupPos);
}

@Override
public Object getChild(int groupPos, int childPos) {
    return items.get(titles.get(groupPos)).get(childPos);
}

@Override
public long getGroupId(int groupPos) {
    return groupPos;
}

@Override
public long getChildId(int groupPos, int childPos) {
    return childPos;
}

@Override
public boolean hasStableIds() {
    return false;
}

@Override
public View getGroupView(int groupPos, boolean b, View view, ViewGroup viewGroup) {
    final String item = (String) getGroup(groupPos);
    Boolean isChecked = allItems.get(item);
    if (view == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = inflater.inflate(R.layout.filter_group_item, null);
    }
    TextView textView = ButterKnife.findById(view, R.id.text);
    textView.setText(item);
    textView.setTypeface(null, Typeface.BOLD);
    CheckBox checkBox = ButterKnife.findById(view, R.id.check_box);
    checkBox.setChecked(isChecked);
    checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
            Boolean isItemChecked = allItems.get(item);
            allItems.put(item, !isItemChecked);
        }
    });
    return view;
}

@Override
public View getChildView(int groupPos, int childPos, boolean b, View view, ViewGroup viewGroup) {
    final String item = (String) getChild(groupPos, childPos);
    Boolean isChecked = allItems.get(item);
    if (view == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = inflater.inflate(R.layout.filter_child_item, null);
    }
    TextView textView = ButterKnife.findById(view, R.id.text);
    textView.setText(item);
    CheckBox checkBox = ButterKnife.findById(view, R.id.check_box);
    checkBox.setChecked(isChecked);
    checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
            Boolean isItemChecked = allItems.get(item);
            allItems.put(item, !isItemChecked);
        }
    });

    return view;
}

@Override
public boolean isChildSelectable(int groupPos, int childPos) {
    return true;
}
}

Problem is that it doesn't work correctly. When I try to play with it some checkboxes unchecked or checked automatically. When I collapse groups by order, and expand them - on this moment checkboxes change their state. Maybe problem is with childId or groupId. But I don't know how to fix it.