Libraries using item groups have to contend with AllowMultipleIssuesOnABiblio, which is currently an all-or-nothing solution, especially if libraries generally only want one issue per record EXCEPT in the case of group holds. I'm not sure if this needs to be a separate permission or a carve out of how AllowMultipleIssuesOnABiblio treats item groups, like it does with records that have subscriptions attached.