In the second post of this series, a proposed answer: that when the gemara and Rishonim say that bedieved it does not work without pirut haneder, they were not speaking of the case where the judges know that the neder is not being specified.
In the third post if this series, I explained Rosh's reasoning for paskening like Rav Pappa, and questioned the first of those reasons, by showing that Rav Pappa was not actually batrai.
In the fourth post, I tackle the second of Rosh's reasons, and how we might cope with Rav Huna apparently holding like Rav Pappa.
In this fifth post, I address the final reason given by Rosh -- that the Yerushalmi seems to hold like Rav Pappa.
As a reminder, here is the Rosh. Click on the picture to see it very large. You want the first column, d"h kasavar.
Rosh gives three reasons we should hold like Rav Pappa over Rav Nachman:
1) Rav Pappa is later than Rav Nachman, so he is batrai, and hilcheta kebatrai.
2) Rav Huna holds like him.
3) The Yerushalmi seems to conclude like Rav Pappa that there is such an obligation.
To address the third point:
This Yerushalmi occurs in the 5th perek of Nedarim, 18b:
אית תניי תני צריך לפרוט את הנדר. אית תניי תני אינו צריך לפרוט את הנדר. חד בר נש נדר דלא מרווחא אתא לגבי רבי יודן בר שלום אמר ליה ממאי אישתבעת אמר ליה דלא מרווחא. אמר ליה רבי יודן וכן בר נש עביד דילמא בקביוסטיסא אמר ברוך שבחר בתורה ובחכמים שאמרו צריך לפרוט את הנדר:
A slight, probably unimportant, difference between Rosh's girsa and our girsa of Yerushalmi, but noteworthy since we were speaking earlier about the rabbinic nature of the obligation to delineate the neder -- our Yerushalmi has ברוך שבחר בתורה ובחכמים שאמרו צריך לפרוט את הנדר, while Rosh is missing the word בתורה.
Rosh used the conclusion of the Yerushalmi to show that we hold that one needs to delineate the particulars and circumstances of the neder. But I am not convinced this is sufficient cause to rule like Rav Pappa over Rav Nachman.
Firstly, the Yerushalmi spells out explicitly that there are competing braytas. One says one needs to delineate the neder and one says that you do not need to do so. There was an incident before Rabbi Yudan bar Shalom, and he praises this position requiring delineating the neder.
But this could be for one of two reasons. Either he was uncertain, and this incident convinced him, or else he was of one particular position. Now, Rabbi Yudan bar Shalom was a 4th century Palestinian Amora, which means that he was a contemporary of both disputants, Rav Nachman bar Yitzchak and Rav Pappa. So the fact that Rav Pappa has a corresponding element in Eretz Yisrael is not so convincing. Different Amoraim hold different positions. On the other hand, the fact that the Yerushalmi saw fit to relate this particular incident may be meaningful. It might not be meaningful, but rather was a known incident, and was relevant to relate in this context. But it might indeed be meaningful, as a way for the Yerushalmi to let it be known how this Tannaitic dispute was resolved -- that the chachamim finally decided that there is a requirement to delineate the neder.
Even if the Yerushalmi does relate it for this purpose, the Rif has a principle that the Amoraim of Eretz Yisrael (and perhaps the Savoraim) were greater experts in Yerushalmi than we are (since Yerushalmi was closed before Bavli), and if they did not cite a Yerushalmi which would be at odds with our Bavli, then it is because this is not to be relied upon. Personally, I do not find that argument so convincing, given the difficulty of conveying information from one place to another, and for other reasons I won't specify here, why I think it possible that the Bavli did not know all the details of the Yerushalmi. But if you endorse such a position, this could be a reason for wondering whether the Yerushalmi, if it really is saying this, should be relevant.
One final, parting note. In the Yerushalmi, Rabbi Yudan bar Shalom praises the Hashem who chose the Torah and the Chachamim. But why praise? There are two possible reasons.
(1) That he would have annulled without hearing all the details, and it would have been effective. That is, based on what the person who took the vow said, the vow might have been annulled, and then the person would go on to sin, playing with dice and profiting.
(2) That because of this peice of information held back, he would have thought the vow was annulled, but in truth it would not be annulled.
I would favor the former over the latter, for stylistic reasons and reasons having to do with Rav Nachman bar Yitzchak's concern, but here I will not elaborate.