I don't know what I'm talking about, but I wouldn't be so quick to dismiss proxy issues. In order for `go get` to work, it depends on the meta tags delivered to the client to point to the actual repo url. I inspected github webpage in browser but there are no meta tags so it must be doing some work upfront and determining if the GETVAR from `go` is present first to determine what it should do (i could only guess).
It's possible that bitbucket might be redirecting to its api subdomain and doing other stuff that doesn't agree with your proxy.
Do you have control over the firewall?