Ashes with Mesquite pellets

Thursday evening, I smoked an 18 pound brisket (already trimmed weight). I was sorting thru my bags of pellets in the basement, and came across a couple of bags of mesquite BBQ delight. I smoked the brisket using my usual technique, six hours on 180 and 225 till done. I came out 10 hours after beginning the smoke and discovered the firepot nearly overflowing with ash and some lit pellets on top and the fire still going. Also, there was about a half of inch of ash on the bottom of the smoker. Ash-e-ist pellets I've ever seen. The ash was real fine, like when you have ashes out of a fireplace, really soft and light. Anyway, my conclusion is that maybe mesquite puts out more (and different kind) of ash then the normal pellets. It's funny, as I think BBQ delight is supposed to be 60 percent oak and 40 percent flavor wood, so you'd think it would not make that much difference. See pic of the firepot.