The -U Flag would normally overwrite the youtube-dl-Script by the latest version from github. When github is in maintenance it sends a 404-page which overwrites the youtube-dl-Script.
Adding HTTP status check
Umh... I can't replicate: If the update function hits a 404 (like http://github.com/sdcsckdjn) I get a ERROR: unable to download latest version and the script gets unaffected.
ERROR: unable to download latest version
Suggestions on how to simulate the behavior?
Add a rule to your host file that redirect http://github.com to your own webserver, then create a little webserver that only serv 500 error for any request.
We changed our release system, and this should not happen anymore.