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.

Thanks,