https://bugs.winehq.org/show_bug.cgi?id=52872
--- Comment #4 from Robert Wilhelm sloper42@yahoo.com --- It is an issue with MultiByteToWideChar.
After
char buf[2]; buf[0] = 255; WCHAR ch; MultiByteToWideChar(CP_ACP, 0, buf, 1, &ch, 1);
ch is 0xfffd.