I know it's an older browser but thought I would tell you anyway, it's just something I noticed. IE 11.0.96 pressing the back button sometimes reloads the same page. Happens on my forum and MLF. This is what I did to recreate it

As a logged in user
any category, click on page 3
then click on a thread
click back to forum index
click page 5
click the back button in IE
Page 5 reloads again instead of going to page 3

I have not noticed the same in Opera