profile search with limit listings to group, where group is a parent, yields duplicates in result list

create a group and add contacts to it (Group Parent)
create a second group, indicate the former is a parent, and add contacts (Group Child)
create a profile and limit listings to the parent group
display as profile search and run the search –
the result listing displays duplicated contacts

tested on sandbox: http://drupal.demo.civicrm.org/civicrm/profile/search?gid=8&reset=1

I'm not sure where the behavior is coming from. I've checked the group cache table and they are being constructed correctly – the combined list of contacts are added and there are no dups. I do note that it appears the dupes only occur for records that are part of other groups – though the number of groups doesn't seem to correlate to the number of duplicates in the result list.