I have a Sunburst locust and a thornless cockspur hawthorn both planted in my backyard in 2008. This Spring I noticed both had branches with thorns on them. All of the thorny branches are new growth that grew in the 2012 growing season. I am absolutely positive of the varieties I've planted so I know it's not a case of a mislabeled plant. They are both seemingly very healthy and not under any abnormal stress. I have tried to research this problem and haven't come up with any answers other than someone commenting that stress could cause this. As I said, both seem to be in very good health. The locust only has 2 thorny branches and the hawthorn has maybe 8 branches with thorns at the very tips. I did notice the branch tips on the hawthorn that have thorns are also kind of curled under vs. growing horizontal which is unusual. Does anyone know why this is happening? Should I cut out the thorny branches?

I'm really hoping someone else has experienced this problem and could provide some insight. Thanks! :)