Every once in a blue moon you stumble into some legacy code that uses framesets -with each frame in the set having its own IE specific hacks to make IE think that the frame's contents need to be rendered as IE 6, 7, or 8.
So what's the big deal? Certainly the fine folks at Microsoft would expect this! These rare situations worked fine in IE 9, and as such it should work in 10!
But lo-and-behold, it doesn't! In IE 10, you see a frame that renders as a blank white page, and when you resize the window it's content appears.
In IE 10, all pages rendered as part of a frameset need to be rendered in the same document mode (Either 10, 9, 8, 7 or quirks) -- This means you cannot have one page of the frameset with a X-UA-COMPATIBLE http header set to something other than what the other pages are rendered as.
If one frame is rendered in compatibility mode, all the others must be as well.
The good news is it is a simple fix -- either remove the need for the special document mode, or set the entire frameset to render in the special document mode.