IE bold text + opacity problem

You know how IE's alpha opacity filter ruins boldface text?

<div style="width:100%;
     filter:alpha(opacity=90);
     font-weight:bold;">
  Hello world!
</div>

If you're using IE, you can see the problem in action here:

Hello world!

I discovered this while tweaking the opacity filter function I wrote about earlier.

After much fruitless Googling and consulting with webdev experts, I couldn't find a fix. And like most solutions, I had to stumble upon it at the eleventh hour: adding a background color or image to the container element will fix the IE opacity rendering problem.

<div style="width:100%;
     filter:alpha(opacity=90);
     font-weight:bold;
     background-color:#fff">
  Hello world!
</div>

Here it is again, with the fix:

Hello world!

Hopefully the search engines will find this page and no one will have to suffer as I have ever again.

UPDATE: SZOJ reader Andre points out that this bug probably surfaced when MS introduced ClearType rendering, which probably explains why the bug goes away when "font smoothing" is disabled.