I don't see anything in particular wrong with your code, I assume what's going on is that the library Win32::Internet connects to does caching on HTTP gets where the params are static. I know i've run into similar issues with older verions of microsoft's XMLHttpRequest object.
I'd try some thing like LWP or WWW::Mechanize which allow for more control over your request, and should be able to accomplish what you need. Another thing that may work is preventing caching by adding something like this:
my $url = $INET->FetchURL($addr."&nocache=".time());