tefilla - Why does Mishneh Torah have Shem uMalchut for Yishtabach?

I was looking into the Seder haTefillot as well as other siddurim based on it, and something always bothered me about Birkat Yishtabach, which as most of you know "closes" the Pesuqei deZimra section opened by Barukh She'Amar. In the other nusachot, the closing berakha does not include "Elokenu Melekh haOlam", very clearly marking it as a "short" berakha according to the Mishna, i.e. every single non-initial berakha in a series, such as the Amida, the berakhot before and after the Shema, Birkat haMazon, etc....

However, in the Mishneh Torah, Yishtabach DOES contain the full formula with "Elokenu Melekh haOlam", which is quite unusual in closing berakhot! (Source: http://www.mechon-mamre.org/i/2700n.htm)

יִשְׁתַּבַּח שִׁמְךָ לָעַד מַלְכֵּנוּ, הַמֶּלֶךְ הַגָּדוֹל וְהַקָּדוֹשׁ בַּשָּׁמַיִם וּבָאָרֶץ: כִּי לְךָ נָאֶה יְהוָה אֱלֹהֵינוּ, שִׁיר וּשְׁבָח, הַלֵּל וְזִמְרָה, בְּרָכוֹת וְהוֹדָאוֹת, נֶצַח גְּבוּרָה גְּדֻלָּה תְּהִלָּה וְתִפְאֶרֶת, עֹז מַלְכוּת וּמֶמְשָׁלָה, מֵעַתָּה וְעַד עוֹלָם. בָּרוּךְ אַתָּה יְהוָה אֱלֹהֵינוּ מֶלֶךְ הָעוֹלָם, מֶלֶךְ גְּדוֹל הַתֻּשְׁבָּחוֹת, אֵל הַהוֹדָיוֹת, אֲדוֹן כָּל הַמַּעֲשִׂים, הַבּוֹחֵר בְּשִׁירֵי זִמְרָה, חֵי הָעוֹלָמִים.

Could this have been a scribal error? What would be the rationale for phrasing the final "Barukh Ata Hashem" in its full form?