HTML5 - resolving href="mailto:" based on page's encoding or force utf-8?

Attached is 1251.html. It's a Windows-1251 russian page. Load it and also  
see the source of it, please.

In Firefox, Safari and Opera, I get the following for the resolved .href  
value of the link. (IE8 just shows the value as it is in the source)

<mailto:?Subject=%D0%9C%D0%B0%D0%B9%D0%BE%D1%80%D1%83%20%D0%95%D0%B2%D1%81%D1%8E%D0%BA%D0%BE%D0%B2%D1%83%20%D0%BF%D1%80%D0%B5%D0%B4%D1%8A%D1%8F%D0%B2%D0%BB%D0%B5%D0%BD%D0%BE%20%D0%BE%D0%BA%D0%BE%D0%BD%D1%87%D0%B0%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D0%BE%D0%B5%20%D0%BE%D0%B1%D0%B2%D0%B8%D0%BD%D0%B5%D0%BD%D0%B8%D0%B5&Body=%D0%9C%D0%9E%D0%A1%D0%9A%D0%92%D0%90,%201%20%D1%81%D0%B5%D0%BD%D1%82%D1%8F%D0%B1%D1%80%D1%8F.%20%D0%9C%D0%B0%D0%B9%D0%BE%D1%80%D1%83%20%D0%94%D0%B5%D0%BD%D0%B8%D1%81%D1%83%20%D0%95%D0%B2%D1%81%D1%8E%D0%BA%D0%BE%D0%B2%D1%83,%20%D1%83%D1%81%D1%82%D1%80%D0%BE%D0%B8%D0%B2%D1%88%D0%B5%D0%BC%D1%83%2027%20%D0%B0%D0%BF%D1%80%D0%B5%D0%BB%D1%8F%20%D1%81%D1%82%D1%80%D0%B5%D0%BB%D1%8C%D0%B1%D1%83%20%D0%B2%20%D1%81%D1%83%D0%BF%D0%B5%D1%80%D0%BC%D0%B0%D1%80%D0%BA%D0%B5%D1%82%D0%B5%20%D0%BD%D0%B0%20%D1%8E%D0%B3%D0%B5%20%D0%9C%D0%BE%D1%81%D0%BA%D0%B2%D1%8B,%20%D0%BF%D1%80%D0%B5%D0%B4%D1%8A%D1%8F%D0%B2%D0%BB%D0%B5%D0%BD%D0%BE%20%D0%BE%D0%BA%D0%BE%D0%BD%D1%87%D0%B0%D1%82%D0%B5%D0%BB%D1%8C%D 
0%BD%D0%BE%D0%B5%20%D0%BE%D0%B1%D0%B2%D0%B8%D0%BD%D0%B5%D0%BD%D0%B8%D0%B5,%20%D0%BF%D0%B5%D1%80%D0%B5%D0%B4%D0%B0%D0%B5%D1%82%20%D0%98%D0%A2%D0%90%D0%A0-%D0%A2%D0%90%D0%A1%D0%A1.%20%0D%0A%D0%9F%D0%BE%D0%BB%D0%BD%D0%B0%D1%8F%20%D0%B2%D0%B5%D1%80%D1%81%D0%B8%D1%8F%20%D1%81%D1%82%D0%B0%D1%82%D1%8C%D0%B8%20%D0%BD%D0%B0>

However, should I instead be getting:

<mailto:?Subject=%CC%E0%E9%EE%F0%F3%20%C5%E2%F1%FE%EA%EE%E2%F3%20%EF%F0%E5%E4%FA%FF%E2%EB%E5%ED%EE%20%EE%EA%EE%ED%F7%E0%F2%E5%EB%FC%ED%EE%E5%20%EE%E1%E2%E8%ED%E5%ED%E8%E5&Body=%CC%CE%D1%CA%C2%C0,%201%20%F1%E5%ED%F2%FF%E1%F0%FF.%20%CC%E0%E9%EE%F0%F3%20%C4%E5%ED%E8%F1%F3%20%C5%E2%F1%FE%EA%EE%E2%F3,%20%F3%F1%F2%F0%EE%E8%E2%F8%E5%EC%F3%2027%20%E0%EF%F0%E5%EB%FF%20%F1%F2%F0%E5%EB%FC%E1%F3%20%E2%20%F1%F3%EF%E5%F0%EC%E0%F0%EA%E5%F2%E5%20%ED%E0%20%FE%E3%E5%20%CC%EE%F1%EA%E2%FB,%20%EF%F0%E5%E4%FA%FF%E2%EB%E5%ED%EE%20%EE%EA%EE%ED%F7%E0%F2%E5%EB%FC%ED%EE%E5%20%EE%E1%E2%E8%ED%E5%ED%E8%E5,%20%EF%E5%F0%E5%E4%E0%E5%F2%20%C8%D2%C0%D0-%D2%C0%D1%D1.%20%0D%0A%CF%EE%EB%ED%E0%FF%20%E2%E5%F0%F1%E8%FF%20%F1%F2%E0%F2%FC%E8%20%ED%E0>

in browsers, according to HTML5/web addresses/iri-bis? (That's what I'd  
get in browsers if it was an http link instead)

The reason I ask is that for 'http', browsers use the document's charset  
to resolve the link into a URI, but with 'mailto', they always(by default  
at least) force UTF-8 in this case (which makes things a lot easier for  
passing the data to webmails and other mail clients, which usually want  
percent-encoded utf-8 to decode).

What do HTML5/web addresses/iri-bis say about this exactly? Do they allow  
Firefox, Opera and Safari to do what they do, or do they say that the  
resolving is like http for all protocols?

Or, is this undefined and the browse does what it wants?

Thanks

-- 
Michael