I've been using the 'ampersand-semicolon' codes for years in the body of the post, but they just don't work in the OP. I have to correct something I said, though -- they used to be just blanked out in my browser (Firefox) but now I'm seeing them unconverted -- that is, the ampersand, semicolon and sandwiched text are there, just the way they were written. After the Election Night hack attack, the admins started filtering all special characters in the OP and some in the body of the text -- last I checked, you still can't use super and subscripts (very frustrating for posts in Science) but there have been a few (mostly very quiet) improvements, such as now seeing accents in responses.
Maybe you get other results in other browsers -- if so that would be useful info to share.
(BTW, the post you linked to shows an á just fine, so I doubt it's my browser. Try putting one in the OP of a new post and see what happens.)
In posting this, I was forcibly reminded of something -- if you preview the text, the accents in the title show up. If you post after previewing, they go away.
If you add the special characters and post immediately, they show up. I think they may also vanish if you edit/update the post. UPDATE: confirmed. They vanish from the headline, but not the body, on update.
ETA: I just removed the semicolons. Now I'm not seeing the accents in my own browser (Firefox on Mac). How about specifying what OS and browser you're viewing my posts with ? Because what seems to work for you (I *can* see the accent in the OP) doesn't seem to work for me (I can't *create* an accent in a new OP).