Per your gemspec https://github.com/antpaw/bhf/blob/master/bhf.gemspec
It has a dependency on rails v4 s.add_dependency(%q<rails>, [">= 4.0.0"])
I suspect its related to asset digest. Where the assets are getting compiled as expected with digest but are referred from respective CSS without digest.
Its a possible issue with sprockets-rails discussed here issue#49
non-stupid-digest-assets - not so good but preferred solution
It will copy non-digested assets to /public