Derived resources must not be checked!
Eclipse use the special ancestor 'Derived' for folders and files. Those resources are generated and not the result of the programmer's work. The Checkstyle-website sais: "tool to help programmers write Java code".
Version 5.7.0 (13 feb) too.
Added new filter implementation (activate in Checkstyle section of project configuration)
See branch https://sourceforge.net/p/eclipse-cs/git/ci/366_filter_derived_files/tree/