To recreate: Enable item groups and item group holds, as well as having AllowRenewalIfOtherItemsAvailable set to allow. Create a record with at least one item group, leaving at least one other item on the record available, and check it out to a patron. Ensure this corresponds to a circ rule with renewals available. Place a group-level hold on the same volume you just checked out for a different patron. Log into OPAC as patron with the item, see that you can renew it. Technically, yes, other items on that record are available, but no other items in that group can fill the hold. That renewal should have been blocked.
This is a big issue for our library. Many of our DVD's are broken out into item groups (volumes) as well as Graphic Novel series and some books. So patrons with holds for a specific volume are left waiting through the 2 cycles of renewals before their hold is allocated to them.