We have an 18 month old Black Australorp that about every 2 weeks or so will drop a soft shelled (immature) egg at night while she is on the roost. I assume she is sleeping while she does this. At other times she will lay a normal egg in the nesting area. I'm giving them a commercial ground limestone/crushed oyster shell mix, I'm wondering if I should also add straight crushed oyster shells. Or, does she have a physical problem? Has anyone else had a problem like this?