Buffer.byteLength() is bugged

node version is 0.6.17.

I was trying to get the number of bytes of a character (SO question) but now I'm testing how to get the REAL number of bytes. The REAL number means that if the char has a value greater than 127 it has to be encoded with a leading extra byte (UTF8 wiki).

Please see:

console.log (Buffer.byteLength ("a", "utf8"));  //bytes: 1, UNICODE hex: 0x61 (1), REAL hex: 0x61 (1)
console.log (Buffer.byteLength ("¡", "utf8"));  //bytes: 2, UNICODE hex: 0xA1 (1), REAL hex: 0xC2A1 (2)
console.log (Buffer.byteLength ("↑", "utf8"));  //bytes: 3, UNICODE hex: 0x2191 (2), REAL hex: 0xE28691 (3)
console.log (Buffer.byteLength ("", "utf8")); //bytes: 3, UNICODE hex: 0x24065 (3), REAL hex: 0xF0A481A5 (4)

Here we have 2 possibilities:

1. Buffer.byteLength() returns the UNICODE number of bytes. Example: Unicode for ¡ is 0xA1 (1 byte). If this is true, then the function is bugged because it returns 2 (real length is 2).
2. Buffer.bytelength() returns the REAL number of bytes. Example: Real hex value for is 0xF0A481A5 (4 bytes). If this is true, then the function is bugged because it returns 3 (unicode length is 3).

What do you think? Is the function bugged?