Rails 4, Heroku, Bootstrap - Overrides not working in Production

Rails 4, Heroku, Bootstrap - Overrides not working in Production

I've converted my Rails app to Rails 4. I'm using the Twitter Bootstrap
Rails gem 2.2.6.
My application is working fine locally and in production. When I deploy
everything looks fine. I'm not seeing any errors in my Heroku logs when
browsing the site.
However, while my dev environment is displaying my color customizations
properly, in production it's using the Bootstrap defaults.
I've tried recompiling my assets before each deployment using:
RAILS_ENV=production bundle exec rake assets:precompile
My application.css contains the usual:
*= require_self
*= require_tree .
My overrides are in bootstrap_and_overrides.css.less and look like this:
@navbarBackground: #4466af;
@navbarBackgroundHighlight: #4E7AC7;
@navbarText: @white;
@navbarLinkColor: @white;
@navbarLinkColorHover: #7FB2F0;
All of my other overrides are working correctly. It's just the navbar
that's causing problems.
I've cleared my browser cache/history/etc. and that hasn't fixed it either.
Any ideas? I'm completely stumped.