Not sure if this is a forum issue or a browser issue but I notice the following differences.

When browsing in a Chrome browser, any threads I have not read, are bolded and once read, revert to normal strength.

When browsing in IE (8/9) all threads are at normal strength. I prefer the bold and wonder if there is some compatability issue.

Wonder which is expected and how it works in other browsers?

 

FF and Opera both show bold for new unvisited threads for me.

But you can also use the New Posts button in the top forum tool bar to see any new posts since your last visit.

I think that it is dependant on how the browser displays visited or unvisited links and your cache.

Clear your cache of all cookies/history and see what happens. (I do this systematically on shut down, it's just a habit I got into years ago with Netscape).

I normally use FF, but have just tried a clear out of IE10 and sure enough a new thread was just displayed as bold.

 

Yup, I spot on this as well. When using Chrome I see exactly what you described and forum jump options seem different than it is with IE9 .
IE9 is viewing the pages nicely as supposed to do but still sometimes I need to use Google Chrome to get the forum pages to load because IE9 doesn't refresh the pages ,you just press the button and wait but nothing happens , I dunno why