(147635.4)"The only difference between personal and zone coverage is that matchups on each possession will be slightly randomized when zone defense is chosen"
Perhaps that thread and particularly GM-kozlodoevs words explain the issue a bit for you, though it isnt very clear (the thread).
As I understand it, yes, your PG will be guarding their PG most of the game, but sometimes, randomly, your other players guard him too. And if you set for example your SF to play defence as PG, then he will defend their PG most of the game.
In real life basketball when their PG drives, naturally your C picks him up, but I dont think it works like that in this game. When he drives he'll be still guarded normally (the way I just explained).
Thats what I think. Hope you understand it. Hope it helps :)
Rubbercube