Matching the User-Agent in the Session Class

[eluser]osci[/eluser]
No, I don't think that's your preferred solution.
Maybe as wanwizard stated

Is your HTML bad so that IE falls back to IE7 mode?

or

Do you have some funny emulation mode activated?

Unless ie8 reports as ie8, gets the page, goes into compatibility and reports back as ie7.
Could it be that the one machine you have problem is the only one with compatibility mode on?

And if that's the case, wow, ie does the trick again
Why would we need a browser compatibility view anyway???? (guess, ie developers suck).