Opera, Inevitably Unexpected

Update

Opera fellas works at speed light, the problem described in this post has been patched already, great stuff and thanks!

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Just a quick one, about what I have discovered with Opera 10.62 when I have tested wru against this browser ...

// host object
var xhr = new XMLHttpRequest;

// this is true
alert("addEventListener" in xhr);

// this is undefined
// not even null
// simply undefined!!!
alert(xhr.addEventListener);

The Problem

99% of libraries out there are assuming that key in object is one of the fastest and most reliable way to have features detection.
Today, we know that this assumption is wrong.
It's not about the reproducibility of the problem:

var o = {};
o.key = o.key;
"key" in o && o.key;

It's about an ...

Epic Fail (Already Fixed!)

The engine "behind the scene" is broken. Whatever it happens there, we have a broken chain through pseudo inheritance that exposes publicly a method that does not exist, which brings us down the assumption that host objects are not tested before the release ... or surely not their "apparently valid" methods.
Nothing else to say, come on guys, you've always been pioneer and good fellas, so please don't release these mistakes, thanks.