Hi,
Filter sorting are stored in the user session. So when the user would change the page, the sort type would be the same.
So, if the customer change the category, the sorting would be kept.
The solution is to include the default "sort option" in the url of your categories links. So when the customer would click on it, the sorting would be reset to this value.
After that, when you change the "sort column" or the "sort direction", data is passed thought POST.
It means that a form is submit to your website including all filter options.
That's why, when your browser go back in his history, see that the page were a "POST" page and ask you to re-submit the form.
Regards,