The eZContentOperationCollection::addAssignment method never returns a "falied" status, even when it does not actually add the desired location because the user has not enough permissions to do so.

This is bad because:
. it does not allow a caller to check if operation was succesfull
. it will happily run a workflow on the post-add-location trigger even if the location was not added

Also no error is returned if the new location is not added because it already exists