or get springs which have more tension because yours are worn? Could you have streched them when you replaced the blades... older they are the more fatigued they would get. I woudld not grind down the existing mechanism.

There is a spring which they sell at most common automotive store which simply straps on to your existing system and not needing to remove anything.. try those if nothing else works.

By the way.. does this happen when your at a stand still or driving at moderate speeds. I have noticed that the lighter plastic blades tend to want to take off from the winshield compared to the metal ones.