The gemara, on Berachot 10b:
Or, in English:הקורא מכאן ואילך לא הפסיד:אמר רב חסדא אמר מר עוקבא ובלבד שלא יאמר יוצר אור מיתיבי הקורא מכאן ואילך לא הפסיד כאדם שהוא קורא בתורה אבל מברך הוא שתים לפניה ואחת לאחריה תיובתא דרב חסדא תיובתא איכא דאמרי אמר רב חסדא אמר מר עוקבא מאי לא הפסיד שלא הפסיד ברכות תניא נמי הכי הקורא מכאן ואילך לא הפסיד כאדם שקורא בתורה אבל מברך הוא שתים לפניה ואחת לאחריה
HE WHO RECITES THE SHEMA' LATER LOSES NOTHING. R. Hisda said in the name of Mar 'Ukba: Provided he does not say the benediction of 'Who formest the light'.50 An objection was raised from the statement: He who recites the Shema' later loses nothing; he is like one reading in the Torah, but he says two blessings before it and one after. Is not this a refutation of R. Hisda? It is [indeed] a refutation. Some there are who say: R. Hisda said in the name of Mar 'Ukba: What is the meaning of HE LOSES NOTHING? He does not lose the benedictions. It has been taught to the same effect: He who says the Shema' later loses nothing, being like one who reads from the Torah, but he says two blessings before and one after.The Yerushalmi has neither the position of Rav Chisda nor the disproof from a brayta, that says that one does not lose out means that he does not lose out on the brachot.
Focusing just on the first lashon of the gemara (which I happen to think is the correct one -- more on that later), there seem to be two ways one can understand the מיתיבי, the objection from a Tannaitic source. The first (a) is that the quote from the Tannaitic source is:
הקורא מכאן ואילך לא הפסיד כאדם שהוא קורא בתורהThat is, the disproof is from the Mishnah. And the gemara elaborates by making a diyuk as to what it is that he does not lose, and that is that he does not lose the brachot. And therefore,
אבל מברך הוא שתים לפניה ואחת לאחריה(This is then parallel to Mar Ukva's deduction from the Mishnah in the second lashon.)
The other way of reading it (b) is that this is a full citation from a brayta (which does not occur in Tosefta or Yerushalmi, which is certainly plausible). And then, it is a simple contradiction to Mar Ukva.
Rashi explains the Mishnah, or perhaps Rav Chisda's position, as follows:
הקורא מכאן ואילך לא הפסיד. שהרי הוא כאדם שקורא אחת מכל הפרשיות שבתורה ואע"פ שלא יצא ידי ק"ש יש לו קבול שכר כעוסק בתורה:It would seem that Rav Chisda does understand the Mishna, that he does not lose out, to mean that he does not lose out entirely in his chance to say the Shema. Rather, he can still formally say it, and he is just like one who read the Torah. But that does not mean that he is fulfilling the mitzvah of Kriat Shema, and so he should not say the berachot. That this is indeed a lower level of fulfillment seems to be the implication from the other attributed statement in the gemara that follows, as well as in the parallel discussion in the Yerushalmi.
If we understand the first lashon as (a), then I don't think that the Mishna is the greatest disproof. Rav Chisda / Mar Ukva is interpreting the Mishna in a similar, but different manner. That is, we understand that lo hifsid in the parlance of the Tannaim meant lo hifsid et haberachot. And recall that Mar Ukva did not say ובלבד שלא יאמר הברכות. He said ובלבד שלא יאמר יוצר אור, which is only the first of the brachot. While one could say that יוצר אור is a stand-in for all the brachot, the simplest explanation is not like that. When Mar Ukva says that he should not say Yotzer Ohr, the simplest explanation is that he means only yotzer ohr, but the other bracha before Shema (Ahavah Rabba or Ahavat Olam) as well as the bracha after Shema (of Gaal Yisrael) one does say.
In other words, Mar Ukva is suggesting that one should not say any of the brachot because the mitzvah of kriat Shema has already passed. Rather, it is specifically yotzer ohr which one should not say. Why not? Well, because three hours into the day, Hashem is no longer in the process of creating the light. The light is already present. And one should not say a bracha whose content is no longer applicable.
If so, Mar Ukva quite likely made such a diyuk in the Mishnah. Lo mafsid et haberachot means that one still gets to say Shema with (some) surrounding blessings, as it has been instituted. This of course differs with the gemara's interpretation of the Mishna, that אבל מברך הוא שתים לפניה ואחת לאחריה, he does not lose anything at all, such that he makes two brachot in the beginning, thus inclusive of yotzer ohr.
What if we understand it as (b), that there is an explicit brayta which states אבל מברך הוא שתים לפניה ואחת לאחריה, which then contradicts Mar Ukva?
Well then, we should realize who the author of this statement is. It is not Rav Chisda who is being refuted, as the setama degemara implies when it states תיובתא דרב חסדא תיובתא. Rather, Rav Chisda is citing Mar Ukva. This Mar Ukva was a first-generation Amora, plus a student of Shmuel. The Resh Geluta in the time of Rabbi Yehuda HaNasi, compiler of the Mishnah, was Rav Huna Kamma (meaning Rav Huna the first). After his death, the Amora who took over was (perhaps his son), Mar Ukva. And so we might be dealing with a fairly early tradition being stated by Mar Ukva, parallel to the early Amoraim / quasi-Tannaim such as R' Hoshaya Rabba and R' Chiyya Rabba, who produced the braytot.
What about the second lashon? Well, I say that איכא דאמרי is generally a parallel Talmudic text. (Thus, often, one can see איכא דאמרי in differing attributions of statements, where one can be a scribal error for the other.) In the second lashon, it certainly is clearer that אבל מברך הוא שתים לפניה ואחת לאחריה is part of a brayta which explicitly contradicts the position attributed earlier in the first lashon to Mar Ukva. That is, Mar Ukva is now the one who makes a diyuk from the language of the Mishna [as in my interpretation (a) in the first lashon], and then we discover that there is explicit brayta [as in (b) in the first lashon] which reinforces that diyuk.
However, we lose out the bit about yotzer ohr, which is then only the first of the brachot that Mar Ukva / Rav Chisda was concerned about. And that bit about yotzer ohr rings true, since we can see a good explanation why he would reject that particular bracha out of all three, namely that it is no longer the time of yotzer ohr after three hours.
Based on that, I would select the first lashon as the original. And I also lean heavily towards interpretation (a) within the first lashon. But regardless, I don't see this as such a great tiyuvta to Rav Chisda / Mar Ukva.