I could find a few other notes on Stack Overflow, for instance here and here. I haven't tested it personally yet, but according to the comments, assigning null does nothing on latest IE's and even produces errors on older IE's. Thus this issue may not be specific to IE11, but also impact older IE's.

Also, on the MDN page, we may want to add a reference to an alternative solution: the removeProperty() method (IE9+). It is probably slower than assigning '' to the property, but it might have its use cases, and nevertheless it should be mentioned for the sake of completeness.

I just successfully reproduced the issue, using Internet Explorer 11 and its "emulation mode" in the developer toolbar.

All offered IE versions have the issue: 5, 7, 8, 9, 10, and even 11. (there is no IE 6, not a typo)

Setting to '' removes the style as expected, whereas setting to null doesn't remove it.
Also, I didn't get any JavaScript error in the console.

I'm closing this issue since the IE data was frozen a few releases back.

How about adding a short sentence, still?

Something like:

A style declaration is reset by setting it to null or an empty string, e.g., elt.style.color = null. Note that Internet Explorer does nothing if null is used, it works only with an empty string.