That's really interesting, Sharon. The only thing I can think of is that you have a localized tightning of the fascial sheath with envelops the muscle. I don't know what might be causing this, and why it would be so localized. Does stretching help to alleviate the soreness?
I'm guessing it's happening somewhere on the upper leg? You might try some stretches for the quadriceps muscles, and also for the IT band (which runs from the pelvis to just below knee area long the outside part of the leg)