The Last-Modified header coming from a backend FCGI/CGI script is inspected by util_script.c to enforce RFC2616 (https://tools.ietf.org/html/rfc2616#section-14.29). The Last-Modified header also needs to be compliant with RFC882/1123 as stated in https://tools.ietf.org/html/rfc2616#section-3.3.1, and one important assumption that httpd makes (correctly, as the RFC suggests) is to assume the GMT timezone. If the datestr returned by the FCGI/CGI script is set with a different timezone, then the value might be considered "in the future" and replaced with GMT now() as calculated by httpd. Adding a trace log might help sysadmins while debugging these kind of issues. This is a follow up of r1748379.