The bug:
The randomness of the particle system is not completely random

Repro steps:
1. Create a particle system
2. Set the start colour to a random between two colours
3. Set the start size to a random between two constants
4. Observe how all smaller particles tend to have the same color, and the bigger particles tend to have the other color.
5. See the print screen attached. There are no small red particles for example, and red ones tend to be bigger.