Upgrade to AS 809, there is a patch specifically applied to correct that.

  Locally applied patches:
        ActivePerl Build 809
        22218 Remove the caveat about detached threads crashing on Win
+dows
        22201 Avoid threads+win32 crash by freeing Perl interpreter sl
+ightly later
        22169 Display 'out of memeory' errors using low-level I/O
        22159 Upgrade to Time::Hires 1.55
        22120 Make 'Configure -Dcf_by=...' work
        22051 Upgrade to Time::HiRes 1.54
        21540 Fix backward-compatibility issues in if.pm
  Built under MSWin32
  Compiled at Feb  3 2004 00:28:51
[download]

I see no errors at all using your (modified) code. I'm posting through it now.

In fact, having navigated all the main subhead pages at news.bbc.co.uk, the memory usage is completely stable. The use rises and falls as I navigate, but stays remarkably stable at ~ 13 MB over time.