It seems to always take me back to the previous category I was viewing or back to the all categories page 1.

So for example if I was viewing a thread on 'technics page 4' and then go to a thread on 'bugs page 3' clicking back to forum index will take me back to 'technics page 4'

I have not altered IE settings. I tried deleting cookies.

What settings do you have set in IE or what could I change to test further?

Safari, chrome and firefox work flawlessly for me.