I'm going to defer to the Spring Social community to help out with this, as I'm running a Mac and don't have IE9. Anyone out there willing to help out and try this on IE9 to confirm?
One thing you could try, though, is running the spring social canvas sample (or even the spring social showcase sample) with IE9 and see if you see similar problems. This would help determine if it's a problem with IE9 and Spring Social itself or if there's some other configuration issue in your code.
Also, please note that the spring social canvas sample, although working, does not represent the most idiomatic approach to writing canvas apps with Spring Social. The proper way to deal with canvas apps is to accept the signed request given by Facebook in the initial POST from Facebook and decode it to get the access token; there's no need to go through the authorization process driven by Spring Social's ConnectController or ProviderSignInController. I've got it on my todo list to update the canvas sample, but that just hasn't bubbled to the top of my priorities yet.
I could, I suppose, install Windows on a VM and try it out, but that's going to take a bit of time (and I don't have a Windows disc or ISO handy to install). If I get some time, I might try it...but it would be much faster and more convenient if someone in the community who already has IE9 could help out.
Spring Social Project Lead