The vault rules are reasonable for the simulator but do often result in turn3 : play vault, opponent discards copper and estate, opponent draws estate.
You also see things like: play vault, opponent discards copper and estate, draws silver, now has {bishop, silver, silver, silver} in hand. Opponent plays bishop, trashes silver, buys silver and the vault bot is heading for a win.
This isn't a complaint. We know the simulator has limited decision making and doesn't evaluate combined actions. We can save people's time however so that we don't all have to discover the limitations individually.