It is a character encoding issue, though I am not sure why it is caused.
Websites have character encoding specified in two ways: through the HTTP headers the host server sends when you access the URL, and through the HTML of the actual page. If the two disagree, the HTTP headers override - in general it's good practice for the two specifications to agree.
Apparently, ZetaBoards uses a different encoding (iso-8859-1) on the servers of forums that upgraded from InvisionFree, compared to the encoding (utf-8) on servers for forums that were created as ZetaBoards. You will likely have the same issue in, e.g., TNP's and the LKE's forums, which like Euro both upgraded from IF. You don't have the problem in, e.g., Balder and Osiris, which were created as ZB forums.
Unfortunately, on ZetaBoards forums, we have no control whatsoever over the HTTP headers. So, we are stuck with whatever encoding ZetaBoards has their servers configured for, no matter what encoding we specify on the forum HTML.
EDIT: I posted a support ticket to see whether they can change the HTTP headers for our server.
Websites have character encoding specified in two ways: through the HTTP headers the host server sends when you access the URL, and through the HTML of the actual page. If the two disagree, the HTTP headers override - in general it's good practice for the two specifications to agree.
Apparently, ZetaBoards uses a different encoding (iso-8859-1) on the servers of forums that upgraded from InvisionFree, compared to the encoding (utf-8) on servers for forums that were created as ZetaBoards. You will likely have the same issue in, e.g., TNP's and the LKE's forums, which like Euro both upgraded from IF. You don't have the problem in, e.g., Balder and Osiris, which were created as ZB forums.
Unfortunately, on ZetaBoards forums, we have no control whatsoever over the HTTP headers. So, we are stuck with whatever encoding ZetaBoards has their servers configured for, no matter what encoding we specify on the forum HTML.
EDIT: I posted a support ticket to see whether they can change the HTTP headers for our server.