Minify CSS removes spaces from SVG background-image

In HTML and URL specs, the URL should not contain any space:
https://url.spec.whatwg.org/#url-scheme-string

However this does not seem to be true in CSS: the specs warn that spaces are not accepted in the URLs when not using quotation marks (which would mean that they are allowed as long as we're using quotation marks).

The specs seem to be a bit confused here and this must be why it's a bug with YUI...