Since I've updated to the new Vue 2.1 version I get this message on console:
[Vue warn]: Property or method "_leaving" is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option. (found in component )
But if try again with Vue 2.0 this warning dissapears.
I do not understand, I'm using the default transitions
Just update again, problem has been fixed: see https://github.com/vuejs/vue/issues/4300