(false) WARNING HTTP Error 400 Bad Request for login, but still works

[uruiamme]

Checklist

• I'm reporting a broken site support issue
• [X ] I've verified that I'm running youtube-dl version 2020.01.24
• [X ] I've checked that all provided URLs are alive and playable in a browser
• [X ] I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--download-archive', 'archive.txt', '--prefer-ffmpeg', '--ffmpeg-location', 'R:\\YouTube\\Download\\ffmpeg\\bin', '--restrict-filenames', '--embed-thumbnail', '-f', 'bestvideo[ext=mp4]+bestaudio[ext=m4a]', '--cookies', 'cookies.txt', '-u', 'PRIVATE', '-v', '-i', '--', 'SPoC69OD990']
Type account password and press [Return]:
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2020.01.24
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.17763
[debug] exe versions: ffmpeg N-94303-g7cb4f8c962, ffprobe N-94303-g7cb4f8c962, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] Downloading login page
[youtube] Looking up account info
[youtube] Logging in
WARNING: Unable to log in: HTTP Error 400: Bad Request
[the rest of the logs consist of a normal download and file save]

Description

I normally login because I frequently download videos only available to subscribers on the community tab. However, this was just a normal video. It actually downloaded. I tested a video that I needed login credentials...

DESPITE the warning, the video still downloads in each case, so I think the login is actually ok and the warning is wrong. Let me know if you need the URL of a video that is only available to a member.