[Koha] disallow hold requests to be placed on items that are not checked out

[justin fang]

Hi,

     I have a question to setup "disallow hold requests to be placed on
 items that are not checked out". I find a preference named
"AllowOnShelfHolds" and it works. If the item is not checked out, I will
unable to place a hold on it. BUT if the record has more than one items, I
will ABLE to place a hold on it. For example, there is a record with three
items, one of them are checkout but two are not. I will ABLE to place a
hold on it. Is it correct behavior or is there any setting I missed?

Thanks,
Justin