> For demonstration purposes, take: 
>       <http://www.cygwin.com/setup.exe>

Excellent test case - thanks.

This was a bug in the handling of files not present in the 
cache. It was not exactly a cache bug, but the previous 
format contained the last-modified-date used for update 
process.

The new cache will now use the timestamp stored on the 
filesystem to perform update of broken static files.

I will probably release the patch in the BETA-1 this week-
end.