Been doing some essential fall practise recently indoors. Have a single mammut rope (the cheapo one) in used but reasonable condition. After taking a couple of short (3-4m) falls on it, the area where the rope has run through the upper quickdraw has gone slight hard, flattened, and plasticy - as if it has melted slightly. The sheath is intact and there's no hot spots of particular damage, just this "singed" section over a metre or so.
So...
Is this is a problem?
How much will it decrease the lifetime of the rope by?
Shouldn't ropes be designed to resist that sort of effective, especially given these are very clean falls onto standard quickdraws?
Is there anything that can be done about it, either with the rope usage / care, or falling technique?
Advice appreciated cheers.