Invoice got on hold for over billing

Dear All,

We have setup tolerance based on Quantity and Amount for AP invoice and it is working as expected.

Now system allowing user to enter invoice with reference to PO within tolerance limit.

But when user try to validate invoice, system putting it on hold and later user manually release this hold.

Can you please explain that why system behaving so, because if tolerance it setup and it is working fine, so it should not put invoice on hold.

Your early response will be helpful.

Thanks,

Manish