Code/CPU instructions always work the way the author intends them to assuming it's all been competently streamlined for said purpose and debugged for common failures, so you're probably unlucky or someone changed something somewhere. I'm also curious if the drops on PSO are influenced or by some kind of calculation purely related to time which does not take into considerations your kill count. I was really lucky few days ago when a relatively unimpressive item with a 1/8130 rate dropped on the first ten kills of an enemy.