In building an HTTP proxy I found that when I aggressively time out the backend requests
and have many client connections, I often get HTTP protocol errors and incorrect
responses.

This is reproducible using httputil.ReverseProxy as well. The code at
http://play.golang.org/p/ZQDr5M2NRx starts a simple server and proxy, and then uses 50
concurrent clients to make requests through the proxy. The server sleeps for 30ms before
responding and the proxy times the backend request out after 35ms, so many of the
requests cannot be handled in time.

What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.

1. Run the code at http://play.golang.org/p/ZQDr5M2NRx on your local computer

What is the expected output?

Besides the initial logging messages, the only error output I would expect are messages
like this:

    http: proxy error: net/http: timeout awaiting response headers

What do you see instead?

In addition to many timeout errors, I get messages like this:

    Unsolicited response received on idle HTTP channel starting with "H"; err=<nil>

and like this:

    Client: expected "hello", got: ""

That second error messages is one I'm printing out when the client makes what is
apparently a successful request to the proxy but gets back something other than
"hello", which is what the server is responding with.

Which compiler are you using (5g, 6g, 8g, gccgo)?

6g

Which operating system are you using?

Tested on darwin/amd64 and linux/amd64

Which version are you using?  (run 'go version')

go 1.2

Please provide any additional information below.

This came up in a similar context to issue #6995. The race detector didn't find any
issues in this code for me, though.