6.x-1.3: Resolved imports and paths when saving non-optimized files. This fixes a bug where @imports or url() paths in non-optimized CSS files would not be resolved because the lived in the "skin" directory and the references were thus broken. You can now safely choose "Save a copy of all CSS and JS files" at admin/settings/skin.
6.x-1.4: Fixed bug introduced in 1.3 which resolved paths in non-optimized JS files, which could cause problems in some cases.
Note: If you had "Save a copy of all CSS and JS files" checked, you may need to clear your existing skins for this change to affect new skin files.