I find it annoying when a new window pops up when I click on forums from the homepage. Especially if I was in the forum to begin with and mistakenly clicked on home and then forums.
I usually prefer it when sites spawn new windows myself, but in this case you may be right. It seems that there is no reason to keep the home page window when going to the forums.
I will get this fixed when I redesign the site. It is currently hard coded to open the link in a new window, many browsers can't override this.