hebrew - Why דָּת in Esther but דַּת in kidushin?

There are two places "דָּת" appears in Tanach in a form that means "the law of": Esther 2:12 and 9:13. In both places it appears as "דָּת" with a kamatz.^[1]

Yet, when we marry, according to the ArtScroll sidur, we say "הרי את מקדשת לי בטבעת זו כְּדַת משה וישראל", with a patach. (That's as we might naively have expected from pairs like שֻׁלְחָן ("table", Psalms 78:19) and שֻׁלְחַן ("the table of", Malachi 1:7^[1]).)

What gives?

• Is ArtScroll simply wrong?


• Or is there a grammatical distinction to be made between Esther and the marriage ceremony which affects the vowel to be used in "דת"?


• Or did Hebrew change (in this respect) between Esther's time and the composition of that line in the marriage ceremony?


• Or what?

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^{1. Possibly of interest, it appears there without a following makaf. I'm not sure what, if anything, the relevance of that fact is.}