In the box, when I type that character (Mac OS X, U.S. keyboard), I get see an ampersand in the editing box: &. What will happen when I post? It posted as ">". Very well, what will happen if I type an ampersand, then the three letters a, m, p, then a semicolon? Here goes: & Nope. How about & ? Nope. How about %26? Nope.

One more try: these are some characters that look like ampersands but have different Unicode code.1 is the normal one available on my keyboard. 1) & 2) ⅋ 3) ﹠ 4) ＆ And, we have a winner. Can I just copy character #4 out of the displayed posting and paste it back in here ＆here ＆here, and still have it display correctly? Yes. Notice that I'm cheating in the sense that ＆ isn't actually an ampersand, it is a "fullwidth ampersand," (U+FF06), and this page tells you about it: http://www.fileformat.info/info/unicode/char/ff06/index.htm It says you can produce it in Windows by typing Alt +FF06.

I'm sure that "reserved character for programming the site" is the answer, but usually there's some kind of escape or workaround and often it isn't hard to guess. A common issue is "SQL injection," which is the subject of an XKCD cartoon: https://xkcd.com/327/ However, ampersand isn't one of the characters that needs to be filtered in order to present sql injections. http://stackoverflow.com/questions/1086918/what-characters-have-to-be-escaped-to-prevent-mysql-injections It's clear enough that it isn't a keyboard issue, but that italki is filtering the ampersand character when it appears in an input here--I haven't checked other parts of the site. It might be worth asking italki about this.

Hi Nanren, Does your ampersand only happen on the browser? if so, did you recently install some tools, extensions for your browser or OS, if so, it may cause that I guess.

My laptop's keyboard was the similar issue as yours, I typed some words, and it sometimes didn't follow my needs, my brand is Acer, I sent it back to the repairer, it's hard to repair, and told me it may be related chips, so I gave up. After years, it's recovered by itself. I know that's weird. sometimes people said it's too damp or seldom use it(true, I was) Good Luck!