Description:
------------
It's converting bytes with the 7th bit on to underscores, this breaks UTF-8. The cuplrit is mmc_prepare_key_ex(). This function does:

        for (i=0; i<*result_len; i++) {
                result[i] = key[i] > ' ' ? key[i] : '_';
        }

... to remove control characters, but as chars are signed... those with the high bit on will be negative!

The fix is to manually cast this to unsigned char before the comparison:

        for (i=0; i<*result_len; i++) {
                result[i] = ((unsigned char)key[i]) > ' ' ? key[i] : '_';
        }

Thanks!