I don't think there's a solution to this one. Microsoft's response is that it's working as designed. I toss it out here more as a public service, to warn others of the trap that's lurking out there. Maybe, with a lot of luck, someone else will figure out how to slay this particular beast.
View this simple page in FF, then try it in IE9: MSNBC Iframe
The page is garbled in IE9, right? The reason is that, apparently, IE9 forces the child page to the same DOCTYPE as the parent page. No matter what. So, this one is a mess because the MSNBC site has no DOCTYPE at all - it's in quirks mode. It doesn't render properly as anything else.
Now before someone beats me about the head and shoulders for using an iframe, let me tell you that it appears to do exactly the same thing with an embedded object.
If you happen to control both the parent and child pages, you can enforce some DOCTYPE discipline. But if you don't, you're basically screwed, as far as I can tell.
Can anyone shed any light on this, like maybe a workaround?