I will guess that you are "strumming" instead of releasing cleanly. It is a form of plucking, except instead of pulling away from your face, you hand is pivoting down at the wrist like you are strumming a banjo. You may have a high drawing elbow when you do this, also. When you use proper form and lower your elbow, your problem goes away. It may happen when you are tired or stressed, your neck, shoulders and back are tight. Try loosening you muscles if it starts happening again. Bill