Encode() Behaves Differently With Different Charsets?

I've recently come upon an odd Javascript (and/or browser) behavior, and after hunting around the Web I still can't seem to find an answer.

Specifically, I have noticed that the Javascript encode() function behaves differently if a codepage has been set.

<script>
document.write(escape('�����'));
(note: that should be five accented characters)
</script>

Produces: %D4%E8%EB%EC%E8

But setting the codepage to Windows-1251:

<META HTTP-EQUIV="Content-Type" CONTENT="text/html;
charset=Windows-1251">
<script>
document.write(escape('�����'));
</script>

Produces: %u0424%u0438%u043B%u043C%u0438

Personally, I wouldn't expect the Javascript encode() function to change its behavior if the codepage has been changed.

Might you know of any resources that can help me better understand what's happening there?