Never seen anyhting like that. I'd take a knife and determine if it is just a thin anti-skid coating or an actual plastic piece bonded to the ends. My engineer's sense is leaning towards the former, which could be removed without too much trouble by scrapping. I wouldn't both cleaning it off of the top, just the bottom.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk