The word "forte" has undergone this change. The actual correct pronunciation of it is "fort" as in a sturdy structure used for defence.
I have only ever heard it pronounced correctly twice, people typically say it as "fortay". This has now become so common that some dictionaries are showing it as a valid pronunciation.
Your belief about which is the "correct" pronunciation depends on whether you believe the "correct" etymology is French or Italian. It appears to me that people agree that the word came into English from French earlier, but also that (at least in 'murica) people have settled on the other pronunciation.
It's not that there's a correct pronunciation that got corrupted, as you suggest. There are two legitimate derivations of this word with different pronunciations and one has won out.
By the way, the word in French would be pronounced \ˈfȯt\, which is a common usage in Britain. And it refers not to a fort (which is the Italian etymology for "a strong point") but rather to the part of a sword between the middle and the hilt.
Source: I like to read about usage and etymology. Sadly my dictionary of classical word origins suggests that forte comes from fortis in Latin, which (while ultimately true) doesn't reflect either later usage or pronunciation.
You are mistaken. There IS a version of "forte" that is correctly pronounced "fortay" and that is the musical term for loud, which is Italian.
The correct pronunciation of "forte" as in an area of strength or speciality is "fort". Older dictionaries will give this as the correct pronunciation but more modern and especially online dictionaries sometimes give "fortay" as an alternate pronunciation.
I used to make that same fort-from-the-french correction until I did so to an Italian girl who looked at me curiously and explained this.
Although I think (in the spirit of pedantry) it's worth noting that the french pronunciation of the word depends on whether it's fort or forte and, of course, the first syllable of the next word!
I have only ever heard it pronounced correctly twice, people typically say it as "fortay". This has now become so common that some dictionaries are showing it as a valid pronunciation.
Language is always evolving, which is great.