Good question. I thought maybe I was lunging farther with one leg but I made sure I was going the exact same distance and I still felt it. Otherwise I can't tell; but at the same distance I can't see where I would be doing it that much differently.
You might want to have someone watch you and tell you if you are doing R and L differently. Or you could always video it and then go back and watch it.
ya this does happen to me with different exercises. my right pec feels it More the the left during chest exercises. my right oblique, i dont even think the thing flexs!
Sounds like everybody has different body mechanics. Different firing patterns from the activities and injuries we accumulated before we started getting really into weightlifting.
Also no one is perfectly symmetrical. Perhaps my left hamstring is like a fraction of an inch shorter than my right or something.