Postprocessors runs after translators and before minifier. BundleTransformer.Core contains the
UrlRewritingCssPostProcessor class that responsible for transformation of relative paths to absolute in CSS-assets. If in the
\configuration\bundleTransformer\core\css configuration element not set the
defaultPostProcessors attribute, then an instance of the
UrlRewritingCssPostProcessor class will added to list of active processors by default. If you have previously used the
disableNativeCssRelativePathTransformation attribute to disable native transformation of relative paths to absolute in CSS-assets, then now you need for this purpose use the
defaultPostProcessors attribute (set an empty value or remove
UrlRewritingCssPostProcessor from a comma-separated list).