This started occurring after the major 2.3 update.
Gaining an amount of XP that would normally give you multiple levels instead only gives you a single level and 99% XP to the next level.
Steps to recreate:
- Set yourself to level 1
- Set your overall and kill XP to x10
- Kill a croc or something
- You will be level 2 with 99% XP to the next level