I'm finding other issue with the Maven Resource Dependency Plugin that makes the generated XCSS file unusable. (The following is true regardless of compression or org.ajax4jsf.xmlparser or org.ajax4jsf.COMPRESS_STYLE settings)
*When aggregating CSS files using the or the configurations, the CSS definitions pulled into the resulting custom-dependencies.xcss file are not nested in a <f:verbatim> tag. As such, when the resource is pulled into the browser those CSS definitions are removed. If the custom-dependencies.xcss file is edited manually and the <f:verbatim> tag is added to surround the CSS definitions, the CSS definitions are not parsed out of the file and the page renders as intended.
*Any occurrence of the ampersand ('&') special characters found in a CSS file throws an SaxParser exception. Consequently using CSS expressions prevents the file from being generated. I know its a bad practice, but I need to support it.