Android :: Query Membership Not Find Contacts In Specific Group

I try to query contacts in a specific group by GroupMembership. But It only works fine with system built-in group "Starred in Android".

My codes is like this:
private static String[] GRP_PROJECTION = new String[] { GroupMembership.PERSON_ID, GroupMembership.GROUP_ID };
Cursor groupCursor = context.getContentResolver(). query(GroupMembership.CONTENT_URI, GRP_PROJECTION, "group_id=" + filterGroup_id, null, null);
Log.d(TAG, "number = "+ getCount());

If filterGroup_id is system built-in group id(Starred in Android), log.d() shows the number of contacts in group. But if filterGroup_id is my self-defined group id, log.d() shows the contacts of person in my defined group is always ZERO! Even there is actually some contacts in my defined group. Is this a bug for SDK1.5 R2?