Hmmm... I've fletched a ton of arrows with feathers and have yet to see one come off on a pass-thru. Rip one through a target bag maybe, but not normally.

One thing I have noticed with feathers is that their base is not always concentric. Check the base of each feather to be sure it is cut properly... squared sides with a level, flat bottom. I've noticed that a number will have bases that are cut on an angle or they will taper radically to one end, or both. Cull those from the bag and you'll have great results with adhesion. I agree with the glue drop method as well... good preventative maintenance.