Disabling enable markdown typographer works as expected.
Posts will keep their … unless you rebuild HTML, since the raw content of the post contains ..
If you want all the posts to have … changed to .., I’m afraid you need to rebake them all after disabling enable markdown typographer (you could select only the posts which the raw contains .. with a rails command though).
Depending on how often this is done, I’d rather fix myself others’ posts and educate the users by asking them using codeblocks 