The newline in `client_cmd` has always been there from the start. Maybe with the recent game releases, it's no more needed.
Are you using the latest HLDS version or ReHLDS?
Also, before anything else, make sure you do pass a valid command and that you can reproduce (create a simple test plugin, if you can)
If you are sure there is an issue and you're using HLDS, you should create an issue on Github