Hi bseng,
The mentioned behavior is expected.
If you like system always running regardless the external interface, you may set wake lock using Legato API or user-space.
For example, set lock on user-space:
echo testlock > /sys/power/wake_lock
To release the lock:
echo testlock > /sys/power/wake_unlock
Please refer to online doc for more info.
http://legato.io/legato-docs/latest/howToPowerMgmt.html
Hope it helps.