Over/Die polishing. Happens quite a bit. Just take a look at the IKE group. This is how the peglegs were formed. Overpolishing on the R.
A similar effect can be seen on parts of the coins in the link, which is filed under "thinning and loss of design elements" by way of die abrasion. http://www.error-ref.com/thinning-and-loss-of-design-elements.html Check out how not all the letters in LIBERTY of the cent are thinned, and some of the other photos there.