Recursive (?) import not working in 2.8

We have a mixins.less (which unsurprisingly contains mixins), a nav.less and a main.less.

nav.less calls a mixin, and main.less includes mixins.less and then nav.less. This used to compile recursively, but now since 2.8 it's throwing an error, saying that the mixin can't be found.

We've rolled back to 2.7 for the meantime. 
