In most long-distance trains, notably in Europe, there are big racks for the larger bags and a shelf above the seats that runs the entire length of the car for smaller ones. The latter is also used for large suitcases when the train is rather full.
Recently, I had put a backpack on the shelf and took appropriate care to position it correctly. Two hours within the ride, while I was not paying attention, my backpack fell on the empty seat next to me. It may have moved with the small shakes of the train at random moments, until it tipped over the edge.
In this case, I was lucky. There was no one in the seat.
But it could have happened otherwise. If the falling bag injures a passenger, or damages a laptop on the tray table for instance, who is liable and what to do?
This can especially happen in double-decker trains where the roof of the top floor is rounded, leaving much less space in the overhead rack. Hours ago, I saw a similar incident happen on board a German ICE, as the train took a turn at high speed and the centrifugal force was enough to move the item off balance. In different situations, a slanted stretch of tracks can cause the bags to slide off.
This is why I am wondering if bearing full liability would be the standard, or if the railway can be involved for "bad" shelf design.