"+" (plus) in filenames causes 400 error

[M-Pixel]

Attempting to upload files with S3-illegal characters in the filename does not typically cause any problem. For example, I can upload objects with "&" in the name. However, files containing "+" in the name fail with a 400 error which reads "Header 'x-amz-content-sha256' set to the hex-encoded SHA256 hash of the request payload is required for AWS version 4 request signing, please set this on: PUT".

Of course, if this is an upstream problem, then I can move the report to Launchpad.