Were you getting any alarms or other indications that something might be wrong?
The motors shut down normally after a few seconds unless you lift off. Not sure what the real reasoning was, but it's generally a good idea. When the drone is on the ground with the props running, it is fairy easy to tip over. You mentioned "a few seconds". If you can clarify how many seconds, it would help to understand if you are getting the normal shutdown, or if something is actually wrong. I believe the time delay is 5 seconds, but perhaps someone can correct me if that is not right.