IE11 and WebGL - broken?

I just recently read that Microsoft is praising its Internet Explorer 11 for its speed and feature completeness. Unfortunately, somehow I cannot agree, specifically when it comes to WebGL, which is now also supported in this latest browser version, which you get when you update to Windows 8.1.
In short: Somehow, on all my test systems, nearly all WebGL demos I try in IE11 are comparably slow, and look completely buggy. In contrast to when run in Google Chrome or Firefox. Here is an example:


This is from the CopperCube Dynamic Light demo, a very small, simple scene demonstrating dynamic light and normal maps.
Another example:


This is from the Backyard demo, an a bit bigger scene. Obviously, some shaders are not running correctly at all. I get a similar behavior from other demos around the web. In some cases, even some parts of the 3D scenes where completely missing, or displaying garbage.

I tried this on three different systems, all with NVidia hardware unfortunately (would like to try IE11 on some AMD device). On two of my systems, most demos look broken. On one of them, IE isn't even able to compile the necessary shaders for the demos and fails running it completely.

I wonder if I am very unlucky, and this only happens for me, or if other people also discovered similar problems. Maybe not many people have upgraded to Windows 8.1 yet, who knows.
Since I'm the author of CopperLicht, I'll try to take a deeper look into the problems causing this very soon.

Update: After seeing this blog post, Microsoft contacted me and told me they will look into this issue and try to improve the situation. Let's see. :)