Gitlab URLs not using the correct port number (non standard HTTP port 8000)

Gitlab skips the port number mentioned in external_url

Details: I have setup gitlab CE in my local environment and my external url setting is

external_url 'http://myurl:8000/'

steps to reproduce issue:

1. open gitlab http://myurl:8000/
2. then gitlab will automatically redirect to sign-in page http://myurl/users/sign_in which is wrong. it skips the port 8000. as a workaround I always have to type in port 8000 in the url.

same issue is happing on sign out: gitlab again redirect to signin page skipping the port.