Verified answer

Yes, there is a special rule. That letter is the final chet (the chet that occurs at the end of a word). Most letters cannot take a vowel at the end of the word. The final chet can, and the pronunciation is reversed when this happens.

Compare with סְלִיחָה

The chet is not a final chet. It is followed by the hey, so it s'liychah.

@Frank's answer isn't very satisfying. And he didn't answer your question about the placement of the "A".

Consonants are a bit difficult to pronounce without a vowel, especially guttural ones (ח, ה, ע) at ends of words. So in this latter case an "A" vowel is appended to the vowel *preceding* them. That's why we pronounce "Mashiach", not "Mashicha": the "A" isn't on the ח but ahead of it.

(Why "A" and not some other vowel? Because it's the easiest vowel to pronounce next to gutturals: the tongue is at its lowest position in the mouth, close to the throat, in proximity to where the gutturals are effected.)

You ask a good question: Why do we write the vowel mark under the ח if it's not intended to be pronounced *there*?

The answer is that this was a limitation of modern printing.

In old handwritings the "A" is indeed written *before* the ח (between the two last letters):

https://www.safa-ivrit.org/g2/gnuva.jpg

However, with modern printing this was somewhat difficult to do and the "A" was printed in the wrong place, an error we perpetuate till today in common printing. However, in modern high-quality printings of the Bible you *will* find the "A" in the correct place.

BTW: you ask, "Why isn't the vowel under the Yod if it's 'Mashiach?'"

That would be an error. An "A" under the yod would mean that the pronunciation is "Mashiyach". That's wrong: it turns the yod into a consonant, which it isn't.

Pronounce Mashiach