"Bad" meaning the arrow could come unsnapped off the string but not fall completely off. Not to mention wrecking any hope for accuracy, it could cause a dry fire and make the arrow whip around, making a mess of your personal tender parts. One of those 'damage to the bow and possible personal injury' things.

Also, are you sure you're not torquing the string or pinching the nock hard enough to lift it slightly off the rest?