Not a Bug Summer Event gives <15% bonus exp

Description of the bug: (optional screenshot/video):
I killed a ribbon pig and got 40 exp + 5 bonus event exp. 15% of 40 should yield 6. I'm sure this is not a big deal as I haven't seen any discussion about this "bug". It may have gone unnoticed with a patch filled with new content. Regardless, the fact is the bonus exp given does not match the advertised rate here. I thought I should bring light to it.

What is supposed to happen?:
I'm supposed to get 6 bonus event exp. 5 exp is incorrect.

Where did you find and/or notice this bug?:
This affects all monsters.

A step-by-step guide to re-producing this bug (optional):
Kill any monster and check the bonus event exp received (highlighted in yellow). Multiply experience gained by 0.15 and compare.

Extra information (optional): I play on a mac.