The 0560 / 0561 are set up with a strong detent from the factory so that they function best as a flipper. There is some variation from knife to knife, so some of them can be opened with the thumbstud/stop pin, but some of them will be near impossible to open with the stud. If this is a dealbreaker for you, I would recommend trying the knife out in person or explaining this to the dealer who sells you the knife.
This is not a defect in the knife, it is simply the way we tune them at the factory.
- Jim