This is also true for ICE trains in GER/SUI/AUT. Most people just leave their luggage in the racks no matter where they move inside the train. Some are even bold enough to bulid a wall in front of the doors and then to not care when someone has to climb over them to get off or on the train.

Generally speaking (for german trains, I know that it's slightly off topic, but might be useful to others) it is absolutely no problem to leave your luggage unattended, as long as nobody is bothered by the placement of your bags. Especially in the newer ICE trains (class 403 to 415) the overhead stowage capacity is really low, especially near the end of the coaches (where the ceiling is lower) so you might not even have the chance of storing your luggage close to your seat. Additionally, I recommend to place a small piece of luggage onto your seat if you leave the seat (for example for the restaurant) for more than a few minutes to mark it as occupied. Nobody will mess around with your baggage.