Including the photo is called being proactive... since someone was bound to end up asking for that information too.
Now THAT makes a lot more sense! I was getting worried that my Prius was a timebomb waiting to happen if I ever overfilled even 1-2 mm on the stick. So it appears the PCV is at least in part responsible, due to perhaps how the PCV is plumbed and how quickly the head drains back into the block. Under normal engine operation, the drains are probably more than adequate, and the PCV suction and baffle are high enough to avoid oil. I can see flooding the head with fresh oil and it backs up into the PCV and straight into the intake. So I probably would have had the oil-in-intake even if I had only put in 3 litres! Why? I use one of those pour spout adapters on the quart bottles of Mobil 1, and I SQUEEZE the bottle so it empties faster. Oi! That's the way I've filled every car/truck I've ever owned, since I don't like to d*** around with oil changes. Have never had a problem either. This sounds like an easy "problem" to solve. Just *slowly* refill the oil, and as Frank suggested leave the dipstick out too. Thanks Frank!
