POST premature connection close

I have encountered a third-party application which does not cooperate with
the Squid proxy (tried 1.1.20 on Linux and 1.1.21 on Solaris).
Using Apache as a proxy works, however.

The application sends a POST request via Squid.
Squid
- receives the message from the client application
- sends the message to the server
- reads 0 bytes from the client
- closes client and server socket
The answer from the server gets lost, and never reaches the client.

    passConnected: Appending 1040 bytes of content
    comm_set_fd_lifetime: FD 19 lft 86400
    comm_select: 1 sockets ready at 898767316
    comm_select: FD 19 ready for writing
    passWriteServer FD 19, wrote 1263 bytes
    comm_select: 1 sockets ready at 898767316
    comm_select: FD 15 ready for reading
    passReadClient FD 15, read 0 bytes
    comm_close: FD 15
    commCallCloseHandlers: FD 15
    comm_close: FD 19
    commCallCloseHandlers: FD 19

The developers of the third-party application believe that Squid is at fault.
It should interpret "0 bytes read" as end of request, and not close the
connection before transmitting the response from the server.
Are they right? If yes, is a patch available?

-- 
Peter Heimann