I think that is a design feature of the flippers a strong detent lets them build up energy to swing open so when you try to use the thumb studs or spydie hole it can make it a pain.

JYD#176
"dein Gott schickte mich zu zerstören"
"Sic semper evello mortem Tyrannis"
"Sometimes the chance of a zombie outbreak is the only reason I need to make many of my life's Decisions." General Delivery