[TYPO3] RealURL sometimes fails or works on the exact same URL

[Martin Seebach]

Best illustrated with a log-exerpt:

80.162.136.186 - - [13/May/2008:17:39:32 +0200] "GET 
/emner/krige/koebenhavns_bombardement/podcastet_byvandring/efterforloeb_og_fordybelse/
  HTTP/1.1" 404 636 
"http://www.danskhistorie.dk/emner/krige/koebenhavns_bombardement/podcastet_byvandring/" 
"Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.0.3705; 
.NET CLR 1.1.4322; .NET CLR 2.0.50727; Media Center PC 4.0; .NET CLR 
3.0.04506.30; .NET CLR 3.0.04506.648; InfoPath.2)"

80.162.136.186 - - [13/May/2008:17:39:58 +0200] "GET 
/emner/krige/koebenhavns_bombardement/podcastet_byvandring/efterforloeb_og_fordybelse/ 
HTTP/1.1" 200 16101 
"http://www.danskhistorie.dk/emner/krige/koebenhavns_bombardement/podcastet_byvandring/" 
"Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; SIMBAR Enabled; 
SIMBAR={D2085168-224C-442a-8A72-F7EA58EA2614}; .NET CLR 1.1.4322; .NET 
CLR 2.0.50727)"

Note the error-codes - one is 404 and one is 200. On the exact same URL.

I've had this problem a few times, and clearing the RealURL cache and 
the FE cache fixes it, but it's not a sustainable solution.

What could be wrong? TYPO3 4.2.0, but had the same problem on a earlier 
4.0 install.

Regards,
Martin Seebach