@dennisk - what rod are you using. I find that if I use a rod that is rated quite heavy (e.g. Shimano Technium), there is a higher risk of breaking off lighter leader. I observed this fishing for springs in the summer where I found that 10 lb Seaguar would break easily if I'm not careful, while with 12 lb, I can really put the boots to the fish. On the other hand, with my Sage 2106 (which has a much lighter tip than the Technium), I can easily land 10+ lb coho on 8 lb flurocarbon.
I'm still leaning toward checking your knots, but the rod can be a factor.