I confirm what I think is a bug in the software you use.
- In the "advanced" edit mode I can write a lot of characters that are not part of the ASCII set (either pressing a key on my keyboard or typing the Unicode code point of the character if it has no matching key) and when I save they show as they should.
- But if I save from the "not advanced" edit mode, these characters are not displayed and if I edit the post again they have also disappeared from the input text.
For instance (I type this from Firefox):
欨
or:
<U+00B5><U+00BC><U+00BF>
Or for something more esoteric in my signature:
😻 or <U+1F63B>
TIP: to display the smiling cat face with heart-shaped eyes just press together:
Ctrl+Shift+u
then type:
1f63b
and press [Enter]
PS I realize that my answer could be considered slightly out of topic as Simon (or Симон in the Cyrillic alphabet) spoke about the "About me" page and I am speaking about editing posts. But yes some parts of the website are unaffected, as e.g. the signature: mine shows a cat face and to edit the signature the "advanced" mode is not available (but maybe it is on the contrary the only one used there?).
PPS I think that the issue in this thread could the same, or similar.
A least I can display a % (percent sign) here in Advanced edit mode.