The JJ,
I had the same thing happen to my 9' Stweart LSP and it was "suppose" to be a step-up in durability from the traditional foam and fiberglass (E-type epoxy). I rode it for nearly 2 years without a problem...even in overhead Blacks. This Valentines Day, I was paddeling out and turtle dove some MAYBE waist-high breakers and my board broke in half about 2/3 up. A couple of guys and I just stared in disbelief for about 10 mins. I called and sent pics to Stewart about it and they basically said...sorry, that's the power of the ocean! they didn't even offer me a discount on a new one...needless to say I will never buy another Stewart! What I learned is that for most epoxy boards, the traditional open cell styrafoam cores DO have impact strength but are weak in terms of flexibility. Once stressed, will tend to break easily under even small conditions...which is why it probably broke clean. Not wanting to throw another $900 down the drain, I did a little research and found Fletcher Chouinard Designs (Patagonia) out of Ventura and Cardiff, CA.
http://www.fcdsurfboards.com/
They use closed cell syrafoam cores and can put a heavier glass on without increasing weight. They have a core sample in the store and as hard as you press, you can barely make a dent, unlike basic styrafoam or foam cores. Basically, their epoxy boards have greater impact and flex strength. I bought their 9' HP Longboard and I will tell you that I have yet to surf a more responsive, fast, durable longboard and they have the best customer service guys I have ever dealt with. Good luck with Walden and after it is all said and done like me, you will probably want to start a surfboard company since they can never make a crappy product and blame any imperfections on the power of the ocean!