Two Types Of Offerings On Shavuot

 Among the mussaf offerings enumerated in parshas Pinchas the Torah does not mention that the goat offered on Shavuot is a chatas.  The Yerushalmi (Rosh Hashana 21a) says the reason is once one accepts the yoke of Torah sins are not looked at.  However, in this week's parsha it does  mention the korban as a chatas,  וַעֲשִׂיתֶ֛ם שְׂעִיר־עִזִּ֥ים אֶחָ֖ד לְחַטָּ֑את, why can it mention it is a chatas here but not in Pinchas?  The Daas Zekanim in Pinchas (28:30) asks why we don't mention the sair mentioned in Emor in the mussaf prayers of Shavuot?  He explains וי״ל שהם נזכרים בכלל מה שכתוב וביום הבכורים בהקריבכם מנחה בשבועותיכם בגלל המנחה כל אלו באין ולא במוסף.  In other words, there are two different types of korbonat offered on Shavuot.  There are the offerings because it is Shavuot, the day of mattan Torah and then there are offerings to accompany the shtei halechem.  It is the offering that comes because it is Shavuot where chatas isn't mentioned because it is a day of kabbalas Hatorah, we don't mention the sins.  However, in Emor, the Torah is listing the shair offered to come along with the shtei halechem and there chatas can be mentioned.  This is clear from the Rambam as well.  In Ch. 8 of Temmidin U'mussafin he says: בְּיוֹם חֲמִשִּׁים מִסְּפִירַת הָעֹמֶר. הוּא חַג הַשָּׁבוּעוֹת. וְהוּא עֲצֶרֶת. וּבַיּוֹם הַזֶּה מַקְרִיבִין מוּסָף כְּמוֹ מוּסַף רֹאשׁ חֹדֶשׁ שְׁנֵי פָּרִים וְאַיִל וְשִׁבְעָה כְּבָשִׂים כֻּלָּם עוֹלוֹת וּשְׂעִיר חַטָּאת. וְאֵלּוּ הֵן הַקָּרְבָּנוֹת הָאֲמוּרוֹת בְּחֻמַּשׁ הַפְּקוּדִים וְהֵם מוּסַף הַיּוֹם. וְעוֹד מְבִיאִין יֶתֶר עַל הַמּוּסָף בַּיּוֹם הַזֶּה מִנְחָה חֲדָשָׁה שְׁתֵּי הַלֶּחֶם וּמַקְרִיבִין עִם הַלֶּחֶם פַּר וּשְׁנֵי אֵילִים וְשִׁבְעָה כְּבָשִׂים. הַכּל עוֹלוֹת. וּשְׂעִיר חַטָּאת. וּשְׁנֵי כְּבָשִׂים זֶבַח שְׁלָמִים. וְאֵלּוּ הֵן הַקָּרְבָּנוֹת הָאֲמוּרוֹת בְּחֻמַּשׁ וַיִּקְרָא.  One of the שעירים is offered because it is the holiday of Shavuot and the other is offered to accompany the shtei halechem. (Rav Eliyahu Baruch.)  [It is noteworthy that the Chabad nusach of the the mussaf does mention both seirim.  The simple peshat in that would be that even though the sair is offered to accompany the shtei halechem, since it effects a kapparah it is mentioned.  See here.)  [Also see here, especially bottom.]