A single report comes from a preferred WebmasterWorld member that Google's MediaBot, the crawler Google uses to power the AdSense ads are cutting off his URLs right after the .ht of the .html pages.
Here is an export of a portion of his log files:
211.10.xx.xxc - - [30/Nov/2007:13:05:16 +0100] "GET /some-file.html HTTP/1.0" 200 11706 "http://www.example.com/other-file.html" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)" 66.249.72.210 - - [30/Nov/2007:13:05:17 +0100] "GET /some-file.ht HTTP/1.1" 404 2390 "-" "Mediapartners-Google" 66.249.72.210 - - [30/Nov/2007:13:05:18 +0100] "GET /some-file.ht HTTP/1.1" 404 2390 "-" "Mediapartners-Google"
You can see that Mediapartner-Google is generating 404 pages on his site by breaking the filename after the extension.
Is this an isolated issue for this user in particular or more wide spread? I tried to validate it on my side but was unsuccessful.
Forum discussion at WebmasterWorld.