Datepicker: Incorrect value for "oo" during Daylight Saving Time

Datepicker's formatDate (http://docs.jquery.com/UI/Datepicker/formatDate) renders dates that occur during Daylight Saving Time as fractions when using the format string 'oo' (three-digit day of the year).

To replicate, attach a Datepicker with the problematic format string to a text (input) box:

$('input#date').datepicker({ dateFormat: 'yy-oo' });

Here is a jsFiddle that does just that: http://jsfiddle.net/X8qDb/

Try to change the date in the text box to "2010-074" (15 March 2010). The Datepicker formats the value using the format string 'yy-oo'. Therefore the text box should display "2010-074" (00:00 15 March 2010). However, the text box displays "2010-73.95833333333333" (23:00 14 March 2010). This is the bug.

The Datepicker behaves this way for all dates that occurred during Daylight Saving Time, which began at 02:00 14 March 2010 and ended at 02:00 7 November 2010 (source: http://eclipse.gsfc.nasa.gov/SEhelp/daylightsaving.html).

The Datepicker also behaves this way for other years such as 2009 and 2011.

A possible explanation of the bug is that Daylight Saving Time made March 14, 2010 last 25 hours instead of 24. Therefore, 00:00 15 March 2010 is in fact 23:00 14 March 2010. If Datepicker selects 00:00 15 March 2010, it will in fact be choosing 23:00 14 March 2010, leading to "2010-73.95833333333333" being displayed.

This bug affects every version of jQuery and jQuery UI (at least up until 1.4.4 and 1.8.7, respectively), on all browsers and operating systems.