In my previous Passo 2007, it can be reset anytime by long pressing button.
Now I have Passo 2011, and it only resets itself after filling petrol.
But there is something behind this, like when i get the tank topped up (from half or less) to full or 7 points, then it resets itself automatically, but if i am at 6th or 7th point and get the tank full, then it does not reset.
But my cousin has Passo 2013 (simple non-hana, non-smart key version), it has a possibility of reset by pressing the button (same as Passo 2007)
So i guess in some years of new shape, maybe from 2010 to 2011/12, it resets automatically upon refill, and then after 2013 models, they started to give this option of manual reset again.
or there might be a possibility that the cars whose meters/mileage are modified lost this manual reset feature, :0 just a guess