转到go.googlesource.com的git clone在代理后面的计算机上失败

Question

I'm trying to clone go package (golang.org/x/text/language, stored on go.googlesource.com) on a RHEL6 server behind a corporate proxy but the go get command fails:

> go get -v golang.org/x/text/language
Fetching https://golang.org/x/text/language?go-get=1
Parsing meta tags from https://golang.org/x/text/language?go-get=1 (status code 200)
get "golang.org/x/text/language": found meta tag main.metaImport{Prefix:"golang.org/x/text", VCS:"git", RepoRoot:"https://go.googlesource.com/text"} at https://golang.org/x/text/language?go-get=1
get "golang.org/x/text/language": verifying non-authoritative meta tag
Fetching https://golang.org/x/text?go-get=1
Parsing meta tags from https://golang.org/x/text?go-get=1 (status code 200)
golang.org/x/text (download)
# cd .; git clone https://go.googlesource.com/text /local/home/me/dev/src/golang.org/x/text
Cloning into '/local/home/me/dev/src/golang.org/x/text'...
error: HTTP response code said error while accessing https://go.googlesource.com/text/info/refs
fatal: HTTP request failed
package golang.org/x/text/language: exit status 128

I'm pretty sure this is related to git not being able to clone as the following command also fails:

git clone --verbose https://go.googlesource.com/text
Cloning into 'text'...
error: HTTP response code said error while accessing https://go.googlesource.com/text/info/refs
fatal: HTTP request failed

I have set proxies both in my shell environment and for git (http and https) and they are working, as you can see here:

wget https://go.googlesource.com/text
--2017-07-04 11:17:15--  https://go.googlesource.com/text
Resolving our.proxy.host ... 10.4.xxx.xxx
Connecting to our.proxy.host|10.4.xxx.xxx|:8080... connected.
Proxy request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: “text”

    [ <=>                                                                               ] 11,014      --.-K/s   in 0.02s

2017-07-04 11:17:15 (622 KB/s) - “text” saved [11014]

go get also seems to work fine, as I'm not getting any problems executing

go get github.com/stretch/testify

Any clues as to what might be the problem are greatly appreciated.

Thanks in advance, Georg