I mean, if the engine sees that the file requested has 
the same size as the one oin cache, then the file is 
considered as "up-to-date" and therefore the 
connection is dropped to save bandwidth.

For the remark on NE, this clearly violate all RFCs 
(1945,2616) and therefore such crap shouldn't be used 
as server. Use Apache :)
Seriously, the hack option can be disabled in such 
cases. But, again, servers who give the script-size 
instead of the content-size are crazy!