I use alot of Spirals, and have seen that effect, for me it usually happens if my blades are too loose, (I discount this in your case since your experienced). The other times i've seen this is when I try to cut thick material. I solved this by using only FD NEW SPIRAL blades. There are other spirals even from FD. But the New Spirals make a big difference especially on thicker stuff. I hope this helps.