Thanks for the feedback!
It hasn't happened for awhile now...probably not since I posted the original message. I'm not certain, but I do think the shells were not very thick. I do give my girls oyster shell, but still seem to get some thin shells from some of my Red Stars. They've only been laying for about a year now, so it seems a bit early to be having problems...yet I do still wonder if they are starting to. Some of the eggs have been a bit oddly shaped, as well as thin shelled. I stepped into the coop yesterday and found one of the Red Stars in the box laying, while her best friend R.S. stayed in there to give her encouragement it seemed. She layed the egg while I was there, and once she was done in the nest box her friend was done too. I think she is the one that has layed a couple of ostrich sized eggs (which had two complete -yolk and white- eggs inside, not just two yolks!), and likely the one that dropped the eggs from the roost.