And now another problem

Just recently the girls have started laying soft shelled eggs. I found one the other day on the highest nesting box where they have never laid an egg before. Today I found two more in the same nesting box. They are more white and flexible then the other egg shells and very fragile. I cracked the first one open and inside it looked like an typical egg.
Not sure what is going on, I looked on line and found this is not uncommon. The remedy is to feed the girls calcium in the form of ground oyster shell or even ground up egg shells. There could be a problem feeding them egg shells in that they love egg shells naturally and may start eating their own eggs. Some recommend not starting them on this path. I'm not sure what I will do. I'm off to the feed store to ask them for advice.