BitFlipper said:

This is what it looks like in WordPad. Compare that to bureX's screenshot where they show the "ClearType" version on the right.

 

Microsoft YaHei in WordPad

I don't know for sure, but I guess the story is like this. Windows normally does indeed render Microsoft YaHei using ClearType. But in the screenshot, Myriad Pro is font-linked to Microsoft YaHei, making it appear to contain Chinese glyphs from Microsoft YaHei. The rasterizer selection logic is apparently unaware of font linking (and probably does not want to know about that, either) and selects the grayscale rasterizer for rendering Myriad Pro as it always does. And thus...