In this week's parsha, במדבר כח:י, the פסוק reads:
'עֹלַת שַׁבַּת בְּשַׁבַּתּוֹ וגו
Why is the סמיכות form (שַׁבַּת) used instead of שַׁבָּת?
Why is shabath kodsh'kha a quirk? Shabath kodesh kodesh is literally "Sabbath of Holiness" (i.e. s'mikhuth), though we understand it and translate it as "holy Sabbath".
It seems the "construct" form is syntactically valid, even where the "stand-alone" form is expected.
Other example that come to mind:
אשת (=אשה) יפת תואר
שכורת (=שכורה) ולא מיין
-Jack Gross
Deep in the heart of Midwood
Similarly in Parshat Emor "מִשְׁפַּט אֶחָד יִהְיֶה לָכֶם".
Just a Masoretic quirk.