ENVIRONMENT and STATS
Win 7
Chrome build number 54.0.2840.99 m (64-bit).

REPRO STEPS
when I tryed to complete the 4th achivement at Google doodle made for hip-hop Birthday, I used one track for both channels 

ACTUAL RESULTS
Achivement reached

EXPECTED RESULTS
It will be impossible to set one track for both channels. It should be two tracks, unique for every channel