Base URL doesn't play nicely with subdomains?

[Lynne]

I recently copied my live site to my test site to do a test upgrade to 3.7.3. All went well but now I'm playing with updating all the templates. One thing I was hoping to change was how I've always had to put full paths in the navbar because of my site setup. I have a main page at www.mysite.org/index.php and then I have my forums at www.mysite.org/forums/. The main home page at www.mysite.org/index.php is a basic vb looking page where I just post some site news and then some recent threads on the bottom. It has the basic vb navbar template and if I left the navbar at default, it would link to member.php and search.php etc. and none of those exist in that directory, so I always went in and changed the paths to "/forums/member.php" and "/forums/search.php" etc. That worked fine for most things but was always a PITA. So, I saw a post by Dismounted suggesting I add the following line in the headinclude template:

<base href="http://test.mysite.org/forums/" />

I did that and then I noticed that when I was on my forums, even though the page source would say the link was to "test.mysite.org/forumdisplay.php", if I clicked on it, it would go to "www.mysite.org/forumdisplay.php"!?! Same thing if I went to a forumdisplay.php page and clicked on a link to a showthread.php page - even though the page source said "test.mysite.org/forums/showthread.php", I ended up on my live site. So, I took that base tag out of the headinclude and all was fine again.

I have now just added the base tag into my home page (head section) at www.mysite.org/index.php and am getting the same problem with all the links to showthread pages there (and links to member pages there). As I said, the page source is fine, hovering over the link says it will go to my test site, but clicking on the link takes me to my live site. The only htaccess I have in my test subdomain is to password protect the test site (per the vb agreement). Can someone explain what I'm doing wrong here?