Codepage 1251 is a single-byte encoding and a superset of ASCII (i.e. ordinals 0-127). UTF-8 is also a superset of ASCII, so there's no problem as long as the encoded text is strictly ASCII. But decoding non-ASCII UTF-8 as codepage 1251 produces nonsense, otherwise known as mojibake. It happens that codepage 1251 maps every one of the 256 possible byte values, except for 0x98 (152). The exception can't be made any clearer.