The sensor will only show as activated and chime on a secondary panel assigned to Smart Area 2. 2GIG seems to make the assumption that if you have more than one partition, you have more than one keypad.
Another option would be to set that sensor as a No-Response type zone, (Sensor type 23) on Smart Area 1, which will never generate an alarm, but will chime and can be activity monitored in Alarm.com via notifications.