Ah! It must be the IE10 engine that solves this. I just tried this from my PC at home via a screen share and I can replicate your findings in IE10 after setting the browser mode as well.
Users without IE10 will still see the issue however, which will of course be the larger portion of IE users for a great deal of time I imagine.
Just when I thought I wouldn’t need to worry about IE9 support anymore too… what an irritating quirk.