Reproduce step:

1. Choose one board with internal speaker and headphone on the same device. (Eg. veyron_jaq)

2. "cras_test_client --dump_s" to see ID of nodes.
        (72a57953)      7:0       100      yes              no  1540521833              INTERNAL_SPEAKER*Speaker
        (9e934263)      7:1        75      yes              no  1540521834              HEADPHONE        Headphone

3. "cras_test_client --add_active_output 7:1" active headphone node.

4. "cras_test_client --rm_active_output 7:0" remove internal speaker.

5. "cras_test_client --dump_s" to see nodes again. We can find there are active nodes now.
        (72a57953)      7:0       100      yes              no  1540522309              INTERNAL_SPEAKER Speaker
        (9e934263)      7:1        75      yes              no  1540522309              HEADPHONE        Headphone


It is also why set_selected_output_nodes function in cras_utils.py sometimes doesn't work.