Re: How can this be?

I'd use Shotput pro software to be safe. The only time I've encountered this problem was when a shot was spanning two cards. The last shot of one card and the first shot of another - typically doesn't always show up in the XDCam browser.

We've lost data in cards before - and found that the card was defective. It was still within a year of purchase but our local Sony office did not want to honour the warranty, claiming that it wasn't covered (although the camera purchased with it was). After a while, they checked the card and found that it was faulty. The first sign is that it doesn't format correctly.

I'd send the card in for checking by Sony - or change the card if it's not a SxS card.