Initially (1.2.x and older), all vars in Clojure were `dynamic` as in they could be rebound thread-locally. In Clojure 1.3, vars need the `:dynamic` metadata to be made dynamic. To ease the transition, in pre 1.3.0 Clojure, vars with earmuffs were automatically declared as dynamic with an warning. That behaviour is now gone in 1.3.0 and thus the new warning.