There IS some kind of bug. I often see status 404 logged in my access log where a 404 could not have happened:
66.249.65.232 - - [12/Oct/2006:16:13:39 +0200] "GET /topic/13442 HTTP/1.1" 404 - "-" "Mediapartners-Google/2.1" "www.mikrocontroller.net"
84.162.95.20 - - [12/Oct/2006:16:16:55 +0200] "GET /forum/3 HTTP/1.1" 404 - "http://www.mikrocontroller.net/forum/7" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)" "www.mikrocontroller.net"
I could reproduce the problem once:
88.65.114.42 - - [12/Oct/2006:16:27:14 +0200] "GET /forum/7 HTTP/1.0" 404 - "-" "ApacheBench/1.3d" "www.mikrocontroller.net"
ApacheBench didn't report a 404.
LSWS 2.2.2, LSAPI 1.11