Imaging is allowing Invoices to overbill POs

We inserted an Invoice through Imaging that had an overbilled PO.

Usually, for the manually inserted invoices, the validation process would put the invoice on hold but, in this case, it let the invoice be validated.

We are assuming that this is the "normal" behavior for Imaging invoices but, was it a bug?

If not a bug, we would like to have imaging invoices also respect this hold validation. Is this possible?

Regards,

Joana