Issue with component recycling?

Hi,

I'm having some problems with this library. After the first transition, the the new child entering the transition group already has the `foo-leave` and `foo-leave-active` classes already set, which breaks the animations. If I patch Preact to disable component recycling (e.g. by making `collectComponent` a no-op), the issue disappears. Am I doing using something wrong here, or is this a real issue?

Test case: https://codesandbox.io/s/72mq76qow6 (click Next Page twice to trigger the issue)