Similar to bug 30324, the hold limits aren't enforced for parent/child item types. A parent limit doesn't seem to matter at all in this case.
The parent/child itemtype feature is currently only used for the number of checkouts.
ah, I misunderstood. I'm renaming this into an enhancement request: Parent and child itemtype hold limits not enforced as expected -> Add hold limits to Parent Child Item Types
We added video games to our collection and is set up to have 6 item types, 3 for new and 3 for regular collection. We'd like to limit the total holds for all 6 item types to 2, no matter if it's Playstation or Xbox New.
Hold limits are enforced for the sum of child item types, but not their corresponding parent or the default: For example, I have two child item types (Audio book and new books) under a parent Book. In my circulation rules, I set Holds allowed (total) for audio books and new books to 1 each and then set my Book rule to 4. I place a hold on an audio book. It successfully prevents me from placing a second hold. I do the same with new books - first hold successfully placed, second prevented. When I attempt to place a first hold on a Book, I get the error Cannot place hold - Too many holds: can only place a maximum of 2 total holds. Koha is only adding the holds allowed from the children item types, not considering the parent or default limits. It is misleading to have the holds allowed (total) columns on child item type circulation rules if they're not enforced in parent/child item type rules.