I really hate to put Dremel down, but my first saw was a Dremel and I broke blades right and left. Scared the living you know what out of me. Not only did the blades break, but bent all to heck. Like Steve said, more than likely machine and beginner not knowing what they are doing. However, the side of you blade holder on the machine has set-screws I believe. Those may need adjusting to line your cuts right. The speed of the machine and the type of wood you are using may also be a factor. Also the use of packing tape helps lube the blade and keeps longer and cooler.
These are just suggestions of what I went through. I no longer use a Dremel, but a Shopsmith instead. I sure hope you find an answer.