I moved this section of code

.top-bar-section li.active > a:not(.button) {..... }

below the following section of code in foundation.css

.top-bar-section li:not(.has-form) a:not(.button) {..... }

This has worked for me. Hope it will work in your case also.

Got the exact same issue. At the moment I've had to put
CSS
!important

in front of the background-colour. But it's still not an ideal fix.

I've reported the issue on github:

https://github.com/zurb/foundation/issues/4232