Mike I have the same mower. I have tried different blades, don't spend the money. I'm sure it is a design flaw, especially after reading all the other questions. I removed the safety rubber in the back and that made it easier to pull back.
I have the same problem on my 4 year old HU600L. I agree with the previous posts. I think the best fix is buying a Honda mower with the twin blade. It is very frustrating that Husqvarna can't fix these issues in 4 years. I'm happy with my mower except the mulching issue. I hope someone finds a fix.
Gary my mower is 4 years old and has the same problem. It seams that the engineers don't use their own equipment so they can make it better. I want to sell mine and get a Honda with twin blades.