It's because it thinks the function gotoCompose isn't there. It's commented out, ish (yes in IE, no in everything else?), using in a jQuery function just under #posts div.
That's my guess at least. If that's it, there's nothing you can do, it's a bug. I dislike IE loads, too, especially wrt to styling and not keeping up with css3 things but it's getting better. And with all the other devices available, I now hate other things more (mobiles, all flavours).
I mean, I hate developing for them. I like using them.