method: cc_utf8_get_char() bug?

unsigned short* cc_utf8_to_utf16(const char* str_old, int length/* = -1 /, int rUtf16Size/* = NULL */)

cc_utf8_get_char(0x78);
the result is 0x78;

but
cc_utf8_get_char(0xb0);
cc_utf8_get_char(0x86);
cc_utf8_get_char(0x96);
all results are 0xfff;

why? thanks