Win 2.3.15 :: The timeout specified has expired

[Steffen]

Observing that the error.log  is filling with [http:error] lines, never seen 
with 2.2:

[http:error] [pid 3244:tid 2656] (70007)The timeout specified has expired: 
[client 114.79.60.32:11091] Timeout while writing data for URI 
/download/binaries/httpd-2.2.21-win32-x86-ssl.zip to the client.

New feature ?

Happens when client is downloading partial (206).

What is the "timeout specified" in the line and can it changed ?