Post: Minchas Shai on parashat Korach leads off:
ויקח קרח -- petucha.
This presumably because it is of masoretic interest that the sidra opens with a petucha.
קהת -- the kuf has only a sheva, and so wrote the author of Mikneh Avraham, that the name Kehat is with a sheva, after the pattern of Dedan.
That is, Dedan mentioned several times in Tanach, including:
בראשית פרק כה
So too Or Torah:
But why is he taking pains to point this out? Because apparently there is a bit of a conflict. In the Leningrad Codex we indeed have with a plain, unadorned sheva.
And many chumashim have the same. (You can look at my source round-up to see a bunch.) Still, a few have a chataf kametz instead.
Thus, here is one from 1491:
תנ"ך. תורה. רנ"א. ליסבון
(אשבונה : דפוס אליעזר [טולידאנו], אב רנ"א).
Interestingly, while the Torah text has the chataf kamatz, the Onkelos text has the bare sheva. Also, Bomberg's first Mikraos Gedolos:
And second Mikraos Gedolos:
And so on. Minchas Shai, indeed, often writes to correct error, or to differ with, this Mikraos Gedolos.
Why would we put a chataf kamatz there. An explanation of the chataf phenomenon in general, from a post on Avodah:
There is a following guttural, heh, in Kehat. Maybe some masoretes saw the need to mark it as sheva na? I don't know for certain.
In some words, especially with gutturals, letters and sounds may be elided, slurred or distorted by sloppy speakers. To prevent this, Ben Asher (or others before him as well) saw a need to point out when the sheva'im in syllables in danger of elision were na'im. This was done by placing an appropriate vowel sign next to the sheva na'. In most words the sheva had a slight "a" sound. Hataf-patach is, therefore, the most common reminder that the sheva is na'. In the fewer cases where the sheva had a tint of e or o vowel sounds, they put a hataf segol or hataf-kamatz. Although hataf-hiriks are not usually marked, there are five of them marked in the Keter. I don't remember ever reading of a hataf shuruk in a text but remember that one is shown in a written mesorah, I think the chet in hamechulal. Also, a shortened or weak shuruk often becomes o as when Uziel becomes ha-ozieli (accent on i not on the oz).
Aside from this, try saying Kehat or listen to someone saying it, masiach lefi tumo, and I think you will likely hear a sort of short /u/ sound, of a chataf-kamatz. So they were quite likely encoding what they heard.