#1. "RE: P7100 and folders" In response to In response to 0 Wed 24-Apr-13 02:39 AM by jec6613
This isn't just the P7100, I've also seen my D5100 do it. In both cases, it was caused by the battery disconnecting and reconnecting very quickly.
What seems to happen is that until the buffer is empty, the camera doesn't increment its internal counter as to the picture number to use next. When you momentarily lose battery connectivity, that images in the buffer were not lost and were written out to the card properly, but use the same numbers as ones earlier in the buffer. So, rather than over-write, the camera creates a new folder.
So, are you using a third party battery? Do you have another to try it with?