D300 Image saving question/problem

[Osmo]

Dear All,

I was reviewing some shots on the camera this morning and noticed that I had two different batches of pictures saved on the CF card.

One set had gone up to 169 and then it had started a new set, currently up to 4. All shots are as expected but I've never noticed it do this before - have I inadvertently changed a setting by mistake or is this something else?

Images are large fine jpg.

CF card: Lexar professional UDMA 8GB 300x speed

Any help appreciated.

Thanks
Osmo