I was recently entering some content into a Confluence wiki page that included some non-ASCII characters, such as “→” (U+2192, "RIGHTWARDS ARROW") and “←” (U+2190, LEFTWARDS ARROW). (I can easily type those characters using Alt+Numpad 26 and Alt+Numpad 27 respectively, since my Windows XP machine is set to Code page 437.) However, after saving the document and coming back and looking at it later, all such characters had been changed to inverted (upside down) question mark characters, “¿”.
Investigation revealed that the problem was that the underlying Oracle database to which the content was being saved was set to use the Western European character set ISO-8859-1, as opposed to a more comprehensive character encoding such as UTF-8. Since ISO-8859-1 doesn’t include the “leftwards arrow” or “rightwards arrow” characters, Oracle converted those characters to the inverted question mark instead.
I wanted to share this here since this information might be helpful to anyone encountering a similar issue in a variety of different possible applications, not necessarily just Confluence.