Apples to apples, the cracking I found was on the sinking portion of the 325 grain QD line. No cracking on clear line experienced to date, as a matter of fact the white finish intermediate 444 big game has held up incredibly tough for three years of abuse w/o cracking.
I've seen the material they use for sinking lines crack before on steelhead hybrid exchangeable heads after two or three seasons of hard fishing.
I think it is related to the amount of physical force it sustains, the running line for my Spey rods used to crack near the loop but nowhere else down the line. I would simply construct a new loop and was good as new.
I'll take a look to see where these cracks fall on the overall taper design of the QD.