In my custom module ,in web browser while saving the new record its showing error and form is not going to saved mode also .But data is getting saved in database and i can see that record in Tree view tooo..How it can be possible ???

class VechicleType(osv.osv):
    def create(self, cr, user, vals, context=None):
        ret_id=osv.osv.create(self, cr, user, vals, context=context)
        print "Normally code but i have different scenario   :\t",ret_id
        return True
    _name = "vehicle.type"
    _description = "Vehicle Type Creation"
    _columns = {
        'name': fields.char('Name', size=64, required=True),
        'capacity':fields.char('Capacity',size=64,),
         'unit_name':fields.char("Unit Name"),
       # 'unit_name':fields.selection(_set_units,"Unit Name"),
    }
VechicleType()