Windows 7 Ultimate 64bit, Java 7
I have started Minecraft with the new Launcher, created a new world, and I started with no Experience bar (As seen in the picture).
Steps to reproduce (works for me):
1. Create a new world in Survival mode.
2. You should have no Experience bar.
I tried starting Minecraft multiple times and it still is invisible.
EDIT: It reappers if you earn a full level.
MC-13592 XP bar missing