Just downloaded and installed v2.02 on my iPhone 3GS running iOS4.
I wanted to check out the new calendar picker so edited an existing task that was due yesterday (July 6) but still not complete. In the Task Details screen the due date was displayed correctly, and it was also displayed correctly in the Edit Due Dates screen (shown as 'Custom').
I tapped on the Custom date to display the calendar, tapped on '6' on the calendar to ensure that the due date was not changed, but when it returned me to the Task Details screen, the date was now set to July 5 (the day before). Go back to the Edit Due Date screen and it still shows July 6. Go to the calendar and it still shows July 6 highlighted.
Doesn't matter what I do, I cannot set the date back to July 6. It just won't let me.
Thanks for the bug report. This is related to your timezone and daylight savings time. We will have this fixed in the next update which we will submit to Apple this week. In the meantime, you can work around this bug by using the button in the upper right corner to switch to the old wheel picker.