Incorrectly experience point gain

What's happened:
The experience point gained may different that I really get.

What's I'm expecting:
The experience point gained is what I really get.

How to reproduce:

1. experience set @s 100 levels

2. experience add @s 6 points

3. experience query @s points
   ❌ -> 5 exp points

1. experience set @s 100 levels

2. experience add @s 12 points

3. experience query @s points
   ❌ -> 11 exp points

1. experience set @s 100 levels

2. experience add @s 24 points

3. experience query @s points
   ❌ -> 23 exp points

1. experience set @s 100 levels

2. experience add @s 48 points

3. experience query @s points
   ❌ -> 47 exp points

1. experience set @s 100 levels

2. experience add @s 7 points

3. experience query @s points
   ✔ -> 7 exp points