CCK Date field decrements when edited

Hi everyone,

Background: I have a content type called "person" which has a bunch of CCK fields: Address, email, 3 phone fields, a money field, a private number, a multiple text select, 3 view references, and a date field (day-month-year granularity). If I edit a person and then click "Submit", the date field is decremented by 1 day (which is a problem, since it's a birthday field).

I've noticed that this doesn't always happen. If I create a new person, nothing changes when the person is edited. It only seems to be happening on my more established person nodes (ie, those that actually have almost all of the fields filled).

Has anyone heard of this before? I implement hook_nodeapi in a custom module, but I don't go anywhere near the date field. Might some of the other CCK fields be interfering with it?

Any pointers are appreciated.

Thanks,

Dave