Ketubot 86a: Collecting the Value of the Paper?

The gemara {Ketubot 86a} reads:

גופא אמר שמואל המוכר שטר חוב לחברו וחזרו ומחלו מחול ואפילו יורש מוחל

אמר רב הונא בריה דרב יהושע ואי פקח הוא מקרקש ליה בזוזי וכתיב ליה שטרא בשמיה
אמר אמימר מאן דדאין דינא דגרמי מגבי ביה מיניה דמוחל [דמי] שטרא מעליא ומאן דלא דאין דינא דגרמי מגבי ביה דמי ניירא בעלמא
[הוה עובדא] ואכפייה רפרם לרב אשי ואגבי ביה ככשורא לצלמי
והלכתא כוותיה

To return to the main text: Shmuel said: If one sold a bond of debt to his fellow, and then turned around and forgave it, it is forgiven, and even the heir can forgive.
Rav Huna son of Rav Yehoshua said: And if he {the buyer} is clever, he rattles for him {the debtor} some money such that he {the debtor} will write the bond in his name {before the creditor forgives the debt}.
Amemar said: He {=Rabbi Meir} who judges liability for indirect action would here allow one to collect from the one who forgave, the amount of a valid bond, and one who does not judge liability for direct action would allow collection of only the value of the paper.
[There was an incident] and Rafram compelled Rav Ashi to order collection of it as a beam fit for decorative mouldings.
{Rif}: And the halacha is like him.

I don't understand why according to Amemar, one would allow the collection of the value of the paper. After all, the buyer is in possession of the paper, so what it to collect from the seller?

We might answer that this is intended idiomatically, that he could not collect anything from either the borrower or the creditor, as the paper is a mere scrap, as opposed to a valid shtar. I think this is correct, but as written, it appears to be misused, since he is not in fact collecting anything at all.