I have noticed some odd things in the mussaf for Rosh Chodesh. Especially when it falls on Sabbath. When it is a Holiday (Passover, Pentecost, Sukkot, New Year, Atonement) there is a certain rubric recited. When the Holiday falls on a Sabbath the standard Holiday rubric is used with little "Sabbath phrases" are peppered throughout the rubric due to it being Sabbath. Now Rosh Chodesh is odd, because when it falls on Sabbath instead of it being the standard Rosh Chodesh rubric with the "Sabbath phrases" peppering it is an entirely different rubric. It looks nothing like the standard Rosh Chodesh rubric, but instead - now this is what got me all befuddled - it contains the words of the Holiday rubric! The Holiday rubric on the 5th word is ahavta otanu, v’ratzita banu........qarata. The Rosh Chodesh Sabbath rubric on the 9th word is ahavta otanu, v’ratzita banu........qarata. So why does the blessing have more in common with the Holiday rubric and nothing in common with the Rosh Chodesh rubric, despite the fact it is Rosh Chodesh Sabbath.
According to the Aruch HaShulchan and other authorities, the Musaf for Rosh Chodesh that falls on Shabbat that is printed in most siddurim is in fact incorrect and should be ammended to include the normal form of Shabbat and Yom Tov. Many poskim have recently published responsum agreeing that the nusach should be corrrected. Some suggest the section beginning "kadesheinu b'mitzvotecha" should be inserted right after retzei b'menuchateinu, others suggest putting it closer to the end of the bracha. I know of no cogent explanation for the text as it appears, and assume it was a printer's error that caught on.