Think there may be a bit more info required here; what type of accuracy are you seeing? What's the nature of the flattened edge? Are we talking about a dinged case mouth from extraction, or something on the face of the case mouth?
Yes it's normal. The case hit the action during extraction denting the mouth. you can slow down the bolt on ejection and that will keep it from happening but i can't see a ton of negative results from it happening.