@jerryThere are many more problems with this website than we care to repeat.  But since we were told by those who know that it's new and improved, in the spirit of emperor's new clothes, I can only tell you that it's nothing but great lest that you should think I'm a nincompoop.

My workaround for your problem, which is really annoying, is to choose to open the thread as a new tab so that the page you're on remains static.  When you're done with the thread you opened, you can then simply close that tab.