My best guess would be that ST drops are regular but still somewhat random (0.01 - 0.1 for example) and drops are definitely calculated after pops. This is the only thing that I can think of that provides some explanation.
I would too appreciate an answer as it is an interesting bug.
On another note - I don`t think that hate and insults help the situation...
BBB: 2 (S37 S38); Top tier: 7 (S35 S36 S37 S38 S39 S41 S63); Cup: 9 (S25 S35 S36 S37 S38 S39 S40 S41 S61)