Currently it's possible for a Sass file, generated in compressed mode, to be re-compressed by Sass. There's a heuristic to avoid that, but it's pretty shaky; if there are any multiline /*! */ comments, re-compression is triggered. Not only is this inefficient, it could potentially cause unexpected and confusing bugs if the generated CSS is something that Sass can't understand as input.
It seems like there should be a more principled way for CssCompressor to avoid conflicting with Sass's compressed mode.
@nex3 That would be a sprocket's issue. They would need to provide a way for a file to be compressed at the same time as it is processed and then to be marked as such. Sass rails must work within the constraints sprockets enforces. I've added the heuristic to speed up the majority of use cases, but I think this bug will need sister bugs in both rails and sprockets in order to achieve this.
cc: @josh @sstephenson @guilleiguaran @wycats
Closing here because there's been no response in months. @nex3 I'll re-open it if it's still present.