The problem is that you are submitting the date with the format: m-d-y
So it might look like: 04-08-05
Well php doesn't know which one of those is the year and which one is the day. It assumes you are using standard database format of y-m-d and it switches the month and the year each time you update.
The solution is to make sure to use a 4 digit date so it can't get confused. I updated the datepicker on the page to use a 4 digit date and that seems to have fixed the problem.