We've noticed that when we've checked the feedback for some of our buyers.
All we can think of is that, if someone has ever sold anything (or at least in the last 12 months) the postage & handlind stars increase with any feedback left, even if it's only as a buyer. Seems to be just another glitch in the system & probably nothing to worry about.
That's only our best guess, though, not really a factual answer.