The above is a link to the w3c's website explaining a particular CSS2 element - "max-height"
This is Microsoft's page comparing the major browsers. Notice how their own product, of course, has more ticks against it than the other browsers.
I could go through each one of those explaining why the missing ticks should not be missing, or why the tick should actually be a cross, but instead I will just focus on the claim that it supports CSS2.1 - admittedly it does not say it supports all of CSS2.1, but the w3c site says that IE supports the property. As do other sites I have visited.
These sites are wrong. IE does not support max-height.
I did a little experiment to prove this. The following pictures are cropped screenshots comparing Google Chrome, Firefox and Internet Explorer 8. They compare how they render a div with the following style settings:
border: 2px solid blue;
Now, what results would you expect from this?
A box with a 2 pixel thick blue border. It will be 50 pixels wide. It's height will be dynamic up to a maximum of 50 pixels. When the content of the box extends beyond those 50x50 limits, scrollbars will appear.
Now, lets look at the results:
That's right, Internet Explorer fails to do what it should, completely ignoring the max-height property.
So, Microsoft, you claim that your browser supports more CSS2.1 than other browsers, but that other browsers support more HTML5 and CSS3 (the things that make CSS2.1 redundant)
All I can say is  - perhaps you should focus on supporting the features your developers will need rather than, at most, obscure features no one who's competent in web design cares about.