I sand the blade ends, use to need to do it before I got the pegas clamps so it is a habit, not sure if I still need to but it has become part of the ritual so to speak..
Whether it is clamp slippage or stretch, I do not know, but once I run the blade for 30 sec or so, it does not happen the rest of the time I use the blade. It is not like I put in the blade, tension it, and cut and done, I do a lot of fretwork so it is cut, release, tension, cut, etc