I added a new task and selected December 9, 2012 as the deadline. However, the text field mistakenly displayed "December 10, 2012 (Sun)" instead of "December 9, 2012 (Sun)".
Sorry for not being clear. I was talking about the iOS app. The bug appeared since the last update.
I opened the app, clicked"Add Task" at the top right corner, entered the task and then pressed "Edit Details". From there I chose "Due date > Custom". I scrolled to December 9 2012 but the text above it showed "December 10, 2012 (Sun)".