Overridden holds in Koha are never trapped unless the reason the hold was forced was due to exceeding the maximum number of allowed holds. If the hold contravenes any other type of rule that would prevent the hold from being placed initially, that hold will never be trapped. So if you allow holds overrides the item will go in to the holds queue, but if you check that item in the box to trigger/trap the hold never appears. So you can never confirm a hold that was created by overriding the rules.
*** This bug has been marked as a duplicate of bug 11512 ***