Replying to [comment:5 lars.feyerabend]:
This fix introduces a serious side effect. People who rely on onSelect to trigger a form submission to the same page will find their page reloading infinitely. For a testcase see here: http://lars-feyerabend.de/datepicker.html
I ran into a similar issue where I was using a datepicker as a navigational tool for a calendar application. I had set it up to redirect the user when a date was selected. Updating from to 1.8.15 caused an infinite redirect loop, just like your example.
Thankfully, binding the redirect function to the change event works as expected. Perhaps that would also work for your form example?
This should certainly be noted in the upgrade guide.