BSONObj o( buf );

>>>  BSONObj.valid() returns false signifying a corrupt BSON object.
            if ( _objcheck && ! o.valid() ) {
                cerr << "INVALID OBJECT - going try and pring out " << endl;
                cerr << "size: " << size << endl;
                BSONObjIterator i(o);
                while ( i.more() ) {
                    BSONElement e = i.next();
                    try {
>>>  e.validate() does not throw an exception and the "NEXT ONE" message is not printed.
                        e.validate();
                    }
                    catch ( ... ) {
                        cerr << "\t\t NEXT ONE IS INVALID" << endl;
                    }
                    cerr << "\t name : " << e.fieldName() << " " << e.type() << endl;

>>>  An assertion is triggered on printing "e" (a BSONElement) to standard error. 
                    cerr << "\t " << e << endl;
                }
            }