Credit hold check not applied, though the limit is passed

Credit hold check not applied, though the limit is passed

Here is the scenario for a customer X with credit limit $25000
credit ccheck rule applied at pick release level(in OM trx type)
and it includes both uninvoiced orders and AR invoices as well.

Customer exposure report for X shows $25,000 available, $0 exposure
create a sales order a , for $24900,book ,pick release it,successfully.
Run,Customer exposure report still shows $25,000 available, $0 exposure. I expect
 the credit exposure to show $100 available.
create a sales order b , for $24900,book ,pick release it,successfully.
Run,Customer exposure report still shows $25,000 available, $0 exposure

So Credit hold check not applied even though the limit is passed ,when