AP - why can fully paid invoice lines be cancelled?

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Hi,

We are using Oracle Cloud Application 19B (11.13.19.04.0).

We have cases where users have gone into a fully paid and validated and accounted AP Invoice - such as in Screenshot1 on image on this post.

The invoice = 228, and the Payment = 228.

The invoice is validated, yet the user can go to Actions > Edit, then select the line and discard it (screenshot 2).

Then system lets them Discard the line, even though the invoice has been paid, etc. etc.

Why would the system let them do that?

Yet - if the invoice as a whole is cancelled - or the user tries to cancel a fully paid invoice - that is not possible (screenshot 3).