If your ears have channel imbalance, your brain would compensate and you wouldn't notice in most cases. Although, in normal life you have natural cross feed enabling the other ear to fill in missing information, not the case with 'phones most of the time. So yes, phones might expose this even with your brain adjusting.
OTOH, maybe you should check whether you have a temporary problem of some sort in one ear., e.g. dare I suggest a mild infection?