Rails asset pipeline -- can't get max-age to set

full problem details posted to SO: http://stackoverflow.com/questions/16096505/rails-asset-caching-cannot-get-max-age-to-set

Long story short, I cannot get the max-age value to set for css or js files. We upgraded to Rails 3.1, so maybe we missed a step along the way? Would love some help as I’ve run out of avenues to pursue on my own.