I just went out and found my first soft shell egg this evening. (Sounds like there are quiet a few of these the last few days) My girls will all be a year in February so they're by no means new layers. I'm going to go by what Ms Prissy said in another post that it's probably just a hiccup in the egg making process and nothing to worry about. That took a huge worry off my mind when I read that.
This is an interesting thread, since I found a soft shelled egg just this morning. My hens don't lay many of them, maybe just three or four since they started laying in August, but every one of them have been laid outside of the nesting area. And all but one was already busted by the time I found it.
Maybe it has something to do with the cold winter weather?
But I'm not sure about that, because I have 2 panel heaters in their coop, which are rigged so that they come on when the thermostat hits 35 degrees and then turn off again when the thermostat hits 45 degrees. Also, I generally let them free range for an hour in the afternoon, but if it is freezing temp outside, then I don't let them go out that day.