Go to Settings --> Accessibility. Then tap Hearing. Towards the bottom, you will find an option for Mono Output, switch that ON. Then you can drop the earphone from one ear.
There is also a left-right sound balance. You can shift the slider to the ear you prefer.
Here is a guide to using the hearing accessibility settings on your phone:
Since it is stock Android, it would be appropriate posting as directed in the link you included in the question. Make sure it's not already reported. If it is, you can either star (you would get mail updates) or add if your observations add more information
In addition, report on Asus official forums too, since you say it is a serious bug.