Last post mysteriously disappearing

Hi all, I have a strange situation, and was wondering if anyone has had similar or can offer any advise.
Basically I have been looking after a blog for friends of mine for a couple of years without incident.
Rachel
Recently the last post has started to disappear, the time interval between post and loss of post varies from days to hours.

I have sort of a theory, but am at a loss as what best to do.
A few weeks ago site was reported as an attack site, I wrote a full post about it here.
I eventually found a bit of unfamiliar javascript in the header.php, and when removed the site was reviewed and cleared by google.
I have tried to tighten security, but i don’t know how it got there, or if there is something else lurking in the code causing the last post to vanish, leaving just post title. At a loss any ideas would be very welcome. Thanks Paul.