Connection error when validating key, behind proxy

Expected behavior

running docker succeeds.

Actual behavior

After entering the token, I get an error

“Put https://validate.docker.com/api: dial tcp 52.4.27.208:443: i/o timeout”

I am aware of specific OSX behaviour and http proxy on the cmd line. (http_proxy env variable is not set, which I set
when working from cmd line with wget and curl). But this is an OSX app, it should use the configured proxy right?

Information

OSX 10.11.5
Behind a proxy on fixed Ethernet. Proxy works fine for http/https in web browser.

Steps to reproduce the behavior

Will be hard to reproduce our specific proxy config. Is this a known issue?