CSS transition is not supported by IE9. So the hooks are not fired. You can checkout the source code here https://github.com/vuejs/vue/blob/dev/src/platforms/web/runtime/directives/show.js#L34

Maybe it should be pointed out in Vue's Transition Effects documentaion. Or add a warnning in dev mode when using hooks in IE9.

So now we have an inconsistency with Transitions in IE9, because hooks were fired when I used v-if instead :)

It shouldn't matter though because these hooks are meant for animations purposes. You can, and should, move other logic to other hooks like created and beforeDestroy

As @zxc0328 noticed, it would be nice to point out in Vue's documentation that Vue's Transitions (not only browser-dependant CSS transitions) are not supported in IE9 . I've tried to use these js hooks only for animation purposes (I wanted to animate elements using js instead of transitions because CSS transitions are not supported in IE9) ;)