We don’t actually have a working undo yet (which is kind of crazy!).
However, if you enter a text-field and edit this, by accident or choice, you can either commit the change by hitting Enter, clicking outside or the field or by zooming out. Alternatively you can hit “Esc” to cancel the change.
Just so I understand you fully:
If a user adds a start-date to an activity, say August the 10th, the date picker (when clicked) for the end-date would default to show August? This to remove some of the frustration of having to skip forwards two months in the picker if the system clock says the current month is June?