After certain HTTP requests cache gives incorrect 404 results for existing files:
82.229.137.15 - - [16/Jul/2010:13:17:24 +0200] "GET /dms/xxxxxx/global/public/homepage%2Dteasers/media_center_homepage_teaser_2.jpg HTTP/1.1" 404 15580 "null" "GbPlugin"

The 404 errors continue until the cache is cleared by publishing a document.

Note the unnecessary %2D and the User-Agent "GbPlugin"

I am not able to reproduce this error with telnet localhost 80
GET /dms/xxxxxx/global/public/homepage%2Dteasers/media_center_homepage_teaser_2.jpg HTTP/1.1
Host: www.xxxxxx.com
User-Agent: GbPlugin

Probably the GbPlugin uses additional HTTP headers which are not logged.

What is the best way to reproduce this? Network sniffer is too much effort. Can apache log requests of a certain User-Agent verbosely?