Netsuite ignoring the date you set, sets its own

I've got a custom record type that has some date fields.  Netsuite is intermittently ignoring the date that I am attempting to set and, without throwing an error of any kind, changing the value that I am attempting to set.  Has anyone ever experienced this?

Example:  I'm pulling the 'trandate' from a transaction record (itemfulfillment).  I'm writing it to one of the date fields on this custom record.  Sometimes it takes what I provided (e.g. 12/11/2013).  Sometimes it ends up 1 day off (12/12/2013, for example).  Sometimes it's 5 days off (12/16/2013).  I know my values are correct, as I'm logging them and verifying in the script logs before I write to the date field.  Yet I see in the resulting custom record that gets created that the value is incorrect.