When I'm on here I "Mark All Read" and leave it on the main forum area, and refresh the page now and again for new posts.
Then I will click one category, see nothing of interest, hit back on my browser and it marks them all as read again.
Is there any fixing this or do I just have to train myself?

Train yourself, since it's in the URL that tells them to be cleared.

I can fix this to not use a URL. I think I put this together in a hurry and that's what I used for simplicity.