Task membership delete does not delete related memberships

I noticed looking at an api test that the behaviour when deleting a membership from a task is different to other forms of deleting (from form, from api)

From the form or api the code is

CRM_Member_BAO_Membership::deleteRelatedMemberships($this->_id);
CRM_Member_BAO_Membership::deleteMembership($this->_id);

but from the task only

CRM_Member_BAO_Membership::deleteMembership($this->_id);

resulting in inherited memberships becoming non-inherited rather than deleted. This seems like a bug but I guess it could be intentional

Neither of these functions is called many times so if the behaviour should be the same wherever the delete is called from I would strongly suggest that we consolidate the function in the BAO layer as a function called 'del' per the standards http://wiki.civicrm.org/confluence/display/CRM/Database+layer
and have the api & forms call that rather than having the same code in several places