read_group does not take inherited fields in its default list-of-fields-to-read, so if grouping on an inherited field it will blow up conversely, read_group can not aggregate on inherited numerical fields, so if it reads *all* the columns (including inherited) it will try to aggregate on fields it's not reading and that's also going to blow up. bzr revid: xmo@openerp.com-20110711113228-18mbcft9y2lf7ptm