Plugin administration: Amazon S3 Settings won't stick

[srdjan-catalyst]

On re-entering the Plugin administration screen one can see that Amazon S3 Settings were not saved.

Also, when entering the screen:
Test connection to the AWS S3 bucket.Could not establish connection to the AWS S3 bucket.Not a S3 exception : Error executing "HeadBucket" on "https://s3.amazonaws.com/"; AWS HTTP error: Client error: HEAD https://s3.amazonaws.com/ resulted in a 400 Bad Request response (client): 400 Bad Request (Request-ID: D9AA76A1C0437081) -
I suspect that's because S3 Settings are missing