Using %20 instead of the plus (+) sign for encoding spaces

I am testing s3fs against a third party s3 storage solution and noticed s3fs-fuse using the plus character to encode spaces in URI. Avoiding the discussion about weither or not this should be ok. I believe the proper way of encoding spaces is the method specified in the HTTP standard, using "%20". 

While Amazon accepts these requests they also say not to use them. 

from Amazon @ http://docs.aws.amazon.com/general/latest/gr/signature-version-2.html

Note:
Be sure to URI encode the GET request. For example, blank spaces in your HTTP GET request should be encoded as %20. Although an unencoded space is normally allowed by the HTTP protocol specification, the use of unencoded characters creates an invalid signature in your Query request. Do not encode spaces as a plus sign (+) as this will cause errors.