The Cortland 444 QD had the same problem, and I haven't heard one bad report on their service policies either. I think it's manufacturing issue caused by the combination of the two materials - sinking head, running line.
The Rio Deep Sea offers the same style line with a much stronger running line union that did not crack or fail for me after most of the season (I used another line early on) and it looks ready for action for this season too.
Frankly, it doesn't shoot like the T series lines or the QD lines, but the cracking problem is more than I could bear.
Luis mentions a new SA line, worth looking into.
I hope someone comes out with a line that shoots as well as the T series / QD lines but is as tough as the Rio.