At a guess, I recently had some websites start refreshing more than I
thought they used to when using the back/forward buttons. From what I
gather, this is due to the websites specifying no-cache or something similar in their HTTP (?) headers. I think reloading the page throws away entered text, while going back/forward to a stored page does not.
Perhaps something the ghc trac is using is setting this? Or it could be something outside trac entirely?
Also wouldn't surprise me if Chrome behaves differently with such a setting than Firefox.
Not sure if that helps.