74860 appearing randomly

Heya,

I've been having trouble lately with the number 74860 popping up from
force-frame javascript on a couple of sites.

The script is quite basic :

if (parent.location.href == self.location.href) {
var myurl = self.location.href;
var lastslash;
lastslash = myurl.lastIndexOf('/');
parent.location.href =
'/content/index.pl?u='+escape(myurl.substring(lastslash+1));
}


where this is put into all of our pages.
Index.pl is a script that as well as other functions, puts everything
in a frameset, with 'u' as the main frame.

Now the problem comes here(from our apache logs) :
1st page, which should be redirected...
/content/main.pl?id=1485&page_id=15&sb=1&tid=1

Page to which it is redirected:
/content/index.pl?u=74860.pl%3Fid%3D1485%26page_id%3D15%26s b%3D1%26tid%3D1

Also with our searchengine rewritten pages:
/content/pp_main_id_2142_page__id_15_sb_1_tid_1.html
becomes
/content/index.pl?u=74860_main_id_2142_page__id_15_sb_1_tid _1.html


This appears to be happening quite randomly, with little or no
consistency in user agents...

I'm quite flummoxed.

Help?

Cheers,
Sam




This is happening seemingly randomly, with no consistency toward
browsers.