'Edit World' and 'Settings' Button Lag

I suffer from the same issue, but also with the settings, save and quit, and resume button. Not that much of a serious bug, but still is present.

I think it's because the screens loads lots of picture resources. What Mojang can do is load all screens at startup/change of resource pack and/or optimize the code so they would load fast.

EDIT: Installing a global resource that has optimized codes for screens will temporarily fix this.